I am trying to solve this problem in JavaScript:
Given an array and a value in JavaScript, find if there is a triplet in array whose sum is equal to the given value. If there is such a triplet present in array, then print the triplet and return true. Else return false.
Now, I wrote some code, and for some reason, it's not working properly.
Here is the code:
A = [1, 4, 45, 6, 10, 8];
sum = 15;
x = A.length;
function find3Numbers(A, x, sum) {
for (i=0; i<(x-2); i++) {
for (j=i+1; j<(x-1); j++) {
for (k=j+1; x; k++) {
if (A[i] + A[j] + A[k] == sum) {
console.log(A[i]);
console.log(A[j]);
console.log(A[k]);
return true
}
return false
}
}
}
}
console.log(find3Numbers(A, x, sum));
Now when I run the code, I get a "false" message.
Any idea, why is that?
You immediately return false if the first triplet you try does not match, when you should only do so after all loops have finished.
A = [1, 4, 45, 6, 10, 8];
sum = 15;
x = A.length;
function find3Numbers(A, x, sum) {
for (i = 0; i < (x - 2); i++) {
for (j = i + 1; j < (x - 1); j++) {
for (k = j + 1; x; k++) {
if (A[i] + A[j] + A[k] == sum) {
console.log(A[i]);
console.log(A[j]);
console.log(A[k]);
return true
}
}
}
}
return false;
}
console.log(find3Numbers(A, x, sum));
Consider sorting the array beforehand for O(n^2) time complexity rather than O(n^3).
Note: O(nlog(n) + n^2) is asymptotically the same as O(n^2).
const find3Numbers = (nums, nums_length, target) => {
nums.sort((a, b) => a - b);
let i = 0;
while (i < nums_length - 2) {
let j = i + 1;
let k = nums_length - 1;
while (j < k) {
curr_sum = nums[i] + nums[j] + nums[k];
if (curr_sum < target) {
j++;
while (j < k && nums[j] == nums[j - 1]) {
j++;
}
} else if (curr_sum > target) {
k--;
while (j < k && nums[k] == nums[k + 1]) {
k--;
}
} else {
return [nums[i], nums[j], nums[k]];
}
}
i++;
while (i < nums_length - 2 && nums[i] == nums[i - 1]) {
i++;
}
}
return [-1, -1, -1];
}
const A = [1, 4, 45, 6, 10, 8];
const x = A.length;
const sum = 15;
console.log(find3Numbers(A, x, sum));
I have an alright understanding of how Heap's Algorithm works, but I can't figure out how to add each unique permutation into an array and return it based on the recursive nature of the algo.
why is it only adding the same permutation but the console log prints out the different ones?
var swap = function (array, pos1, pos2) {
var temp = array[pos1];
array[pos1] = array[pos2];
array[pos2] = temp;
};
var heapsPermute = function (array, n, results = []) {
n = n || array.length;
if (n === 1) {
results.push(array);
console.log(array);
} else {
for (var i = 1; i <= n; i += 1) {
heapsPermute(array, n - 1, results);
if (n % 2) {
var j = 1;
} else {
var j = i;
}
swap(array, j - 1, n - 1);
}
}
return results;
};
console.log(heapsPermute(['a', 'b', 'c', 'd']));
You need to add a copy of the array, instead of the array and it's object reference.
results.push(array.slice());
// ^^^^^^^^
var swap = function (array, pos1, pos2) {
var temp = array[pos1];
array[pos1] = array[pos2];
array[pos2] = temp;
};
var heapsPermute = function (array, n, results = []) {
n = n || array.length;
if (n === 1) {
results.push(array.slice());
} else {
for (var i = 1; i <= n; i += 1) {
heapsPermute(array, n - 1, results);
if (n % 2) {
var j = 1;
} else {
var j = i;
}
swap(array, j - 1, n - 1);
}
}
return results;
};
console.log(heapsPermute(['a', 'b', 'c', 'd']).map(a => a.join(' ')));
.as-console-wrapper { max-height: 100% !important; top: 0; }
I´m trying to implement a quicksort algorithm for an int array in JavaScript.
I´ve got a problem in my code. The first few ints get sorted well but at the end of the sortet array there is always one integer which is placed many times although its only one time in the array which should be sorted. Hopefully someone will find my fault.
Thanks.
function quicksort(array) {
var randomPlace = Math.round(Math.random() * array.length);
var pivotelement = array[randomPlace];
left = new Array;
right = new Array;
for (var i = 0; i < array.length; i++) {
if (array[i] < pivot) {
left[left.length] = array[i];
} else {
right[right.length] = array[i];
}
}
if ((left.length == 0 || left.length == 1) && (right.length == 0 || right.length == 1)) {
return left.concat(right);
} else if (left.length == 0 || left.length == 1) {
return (left.concat((quicksort(right))));
} else if (right.length == 0 || right.length == 1) {
return ((quicksort(left)).concat(right));
} else {
return (quicksort(left)).concat((quicksort(right)));
}
}
Beside some nameming confusion, like pivotelement vs pivot and Math.round vs Math.floor, you need to tackle the problem of for example [1, 1, 1] which is always returning left = [] and right = [1, 1, 1], that calls quicksort([1, 1, 1]) ad infinitum.
To overcome this problem, you need to check for empty left and with right every element, if it is equal to the random pivot. Then return right, without calling quicksort again.
function quicksort(array) {
var randomPlace = Math.floor(Math.random() * array.length),
pivot = array[randomPlace],
left = [],
right = [],
i;
for (i = 0; i < array.length; i++) {
(array[i] < pivot ? left : right).push(array[i]);
}
console.log(pivot, JSON.stringify(array), JSON.stringify(left), JSON.stringify(right));
// prevent looping forever
if (!left.length && right.every(function (v) { return v === pivot; })) {
return right;
}
if (left.length <= 1 && right.length <= 1) {
return left.concat(right);
}
if (left.length <= 1) {
return left.concat(quicksort(right));
}
if (right.length <= 1) {
return quicksort(left).concat(right);
}
return quicksort(left).concat(quicksort(right));
}
console.log(quicksort([2, 7, 4, 8, 3, 11, 49, 20, 10, 1, 1, 1]));
.as-console-wrapper { max-height: 100% !important; top: 0; }
Another solution would be to separate the array into three arrays, one for smaller values, one for equal values and one for greater values. Then sort only the smaller and greater arrays.
function quicksort(array) {
var randomPlace = Math.floor(Math.random() * array.length),
pivotValue = array[randomPlace],
left = [],
pivot = [],
right = [],
i;
for (i = 0; i < array.length; i++) {
if (array[i] === pivotValue) {
pivot.push(array[i]);
continue;
}
(array[i] < pivotValue ? left : right).push(array[i]);
}
console.log(pivotValue, JSON.stringify(array), JSON.stringify(left), JSON.stringify(pivot), JSON.stringify(right));
if (left.length <= 1 && right.length <= 1) {
return left.concat(pivot, right);
}
if (left.length <= 1) {
return left.concat(pivot, quicksort(right));
}
if (right.length <= 1) {
return quicksort(left).concat(pivot, right);
}
return quicksort(left).concat(pivot, quicksort(right));
}
console.log(quicksort([2, 7, 4, 8, 3, 11, 49, 20, 10, 1, 1, 1]));
.as-console-wrapper { max-height: 100% !important; top: 0; }
heres a short version of quick sort written in JS exactly as it is seen in Intro To Algorithms, hope this helps!
var partition = function (arr, low, high) {
var x = arr[high]
var i = low - 1
for (var j = low; j <= high - 1; j++) {
if (arr[j] <= x) {
i++
var temp = arr[i]
arr[i] = arr[j]
arr[j] = temp
}
}
var temp = arr[i + 1]
arr[i + 1] = arr[high]
arr[high] = temp
return i + 1
}
var quickSort = function (arr, low, high) {
if (low < high) {
index = partition(arr,low,high)
if (low < index-1) quickSort(arr,low,index-1)
if (index+1 < high) quickSort(arr,index+1,high)
}
}
var list2 = [1000,13,12,1001,82,1,2,4,3,0]
console.log(quickSort(list2,0,list2.length))
also on my GitHub
I think you are identifying the randomPlace wrongly. It returns undefined some times because you're using Math.round().
Try this instead:
var randomPlace = Math.floor(Math.random() * array.length);
Also, use the following code when initializing left, and right:
var left = new Array();
var right = new Array();
Also, you need to change the pivot in array[i] < pivot to pivotElement.
You can see my complete fiddle here
I am in mid of my JavaScript session. Find this code in my coding exercise. I understand the logic but I didn't get this map[nums[x]] condition.
function twoSum(nums, target_num) {
var map = [];
var indexnum = [];
for (var x = 0; x < nums.length; x++)
{
if (map[nums[x]] != null)
// what they meant by map[nums[x]]
{
index = map[nums[x]];
indexnum[0] = index+1;
indexnum[1] = x+1;
break;
}
else
{
map[target_num - nums[x]] = x;
}
}
return indexnum;
}
console.log(twoSum([10,20,10,40,50,60,70],50));
I am trying to get the Pair of elements from a specified array whose sum equals a specific target number. I have written below code.
function arraypair(array,sum){
for (i = 0;i < array.length;i++) {
var first = array[i];
for (j = i + 1;j < array.length;j++) {
var second = array[j];
if ((first + second) == sum) {
alert('First: ' + first + ' Second ' + second + ' SUM ' + sum);
console.log('First: ' + first + ' Second ' + second);
}
}
}
}
var a = [2, 4, 3, 5, 6, -2, 4, 7, 8, 9];
arraypair(a,7);
Is there any optimized way than above two solutions? Can some one explain the first solution what exactly map[nums[x]] this condition points to?
Using HashMap approach using time complexity approx O(n),below is the following code:
let twoSum = (array, sum) => {
let hashMap = {},
results = []
for (let i = 0; i < array.length; i++){
if (hashMap[array[i]]){
results.push([hashMap[array[i]], array[i]])
}else{
hashMap[sum - array[i]] = array[i];
}
}
return results;
}
console.log(twoSum([10,20,10,40,50,60,70,30],50));
result:
{[10, 40],[20, 30]}
I think the code is self explanatory ,even if you want help to understand it,let me know.I will be happy enough to for its explanation.
Hope it helps..
that map value you're seeing is a lookup table and that twoSum method has implemented what's called Dynamic Programming
In Dynamic Programming, you store values of your computations which you can re-use later on to find the solution.
Lets investigate how it works to better understand it:
twoSum([10,20,40,50,60,70], 50)
//I removed one of the duplicate 10s to make the example simpler
In iteration 0:
value is 10. Our target number is 50. When I see the number 10 in index 0, I make a note that if I ever find a 40 (50 - 10 = 40) in this list, then I can find its pair in index 0.
So in our map, 40 points to 0.
In iteration 2:
value is 40. I look at map my map to see I previously found a pair for 40.
map[nums[x]] (which is the same as map[40]) will return 0.
That means I have a pair for 40 at index 0.
0 and 2 make a pair.
Does that make any sense now?
Unlike in your solution where you have 2 nested loops, you can store previously computed values. This will save you processing time, but waste more space in the memory (because the lookup table will be needing the memory)
Also since you're writing this in javascript, your map can be an object instead of an array. It'll also make debugging a lot easier ;)
function twoSum(arr, S) {
const sum = [];
for(let i = 0; i< arr.length; i++) {
for(let j = i+1; j < arr.length; j++) {
if(S == arr[i] + arr[j]) sum.push([arr[i],arr[j]])
}
}
return sum
}
Brute Force not best way to solve but it works.
Please try the below code. It will give you all the unique pairs whose sum will be equal to the targetSum. It performs the binary search so will be better in performance. The time complexity of this solution is O(NLogN)
((arr,targetSum) => {
if ((arr && arr.length === 0) || targetSum === undefined) {
return false;
} else {
for (let x = 0; x <=arr.length -1; x++) {
let partnerInPair = targetSum - arr[x];
let start = x+1;
let end = (arr.length) - 2;
while(start <= end) {
let mid = parseInt(((start + end)/2));
if (arr[mid] === partnerInPair) {
console.log(`Pairs are ${arr[x]} and ${arr[mid]} `);
break;
} else if(partnerInPair < arr[mid]) {
end = mid - 1;
} else if(partnerInPair > arr[mid]) {
start = mid + 1;
}
}
};
};
})([0,1,2,3,4,5,6,7,8,9], 10)
function twoSum(arr, target) {
let res = [];
let indexes = [];
for (let i = 0; i < arr.length - 1; i++) {
for (let j = i + 1; j < arr.length; j++) {
if (target === arr[i] + arr[j] && !indexes.includes(i) && !indexes.includes(j)) {
res.push([arr[i], arr[j]]);
indexes.push(i);
indexes.push(j);
}
}
}
return res;
}
console.log('Result - ',
twoSum([1,2,3,4,5,6,6,6,6,6,6,6,6,6,7,8,9,10], 12)
);
Brute force.
const findTwoNum = ((arr, value) => {
let result = [];
for(let i= 0; i< arr.length-1; i++) {
if(arr[i] > value) {
continue;
}
if(arr.includes(value-arr[i])) {
result.push(arr[i]);
result.push(value-arr[i]);
break;;
}
}
return result;
});
let arr = [20,10,40,50,60,70,30];
const value = 120;
console.log(findTwoNum(arr, value));
OUTPUT : Array [50, 70]
function twoSum(arr){
let constant = 17;
for(let i=0;i<arr.length-2;i++){
for(let j=i+1;j<arr.length;j++){
if(arr[i]+arr[j] === constant){
console.log(arr[i],arr[j]);
}
}
}
}
let myArr = [2, 4, 3, 5, 7, 8, 9];
function getPair(arr, targetNum) {
for (let i = 0; i < arr.length; i++) {
let cNum = arr[i]; //my current number
for (let j = i; j < arr.length; j++) {
if (cNum !== arr[j] && cNum + arr[j] === targetNum) {
let pair = {};
pair.key1 = cNum;
pair.key2 = arr[j];
console.log(pair);
}
}
}
}
getPair(myArr, 7)
let sumArray = (arr,target) => {
let ar = []
arr.forEach((element,index) => {
console.log(index);
arr.forEach((element2, index2) => {
if( (index2 > index) && (element + element2 == target)){
ar.push({element, element2})
}
});
});
return ar
}
console.log(sumArray([8, 7, 2, 5, 3, 1],10))
Use {} hash object for storing and fast lookups.
Use simple for loop so you can return as soon as you find the right combo; array methods like .forEach() have to finish iterating no matter what.
And make sure you handle edges cases like this: twoSum([1,2,3,4], 8)---that should return undefined, but if you don't check for !== i (see below), you would erroneously return [4,4]. Think about why that is...
function twoSum(nums, target) {
const lookup = {};
for (let i = 0; i < nums.length; i++) {
const n = nums[i];
if (lookup[n] === undefined) {//lookup n; seen it before?
lookup[n] = i; //no, so add to dictionary with index as value
}
//seen target - n before? if so, is it different than n?
if (lookup[target - n] !== undefined && lookup[target - n] !== i) {
return [target - n, n];//yep, so we return our answer!
}
}
return undefined;//didn't find anything, so return undefined
}
We can fix this with simple JS object as well.
const twoSum = (arr, num) => {
let obj = {};
let res = [];
arr.map(item => {
let com = num - item;
if (obj[com]) {
res.push([obj[com], item]);
} else {
obj[item] = item;
}
});
return res;
};
console.log(twoSum([2, 3, 2, 5, 4, 9, 6, 8, 8, 7], 10));
// Output: [ [ 4, 6 ], [ 2, 8 ], [ 2, 8 ], [ 3, 7 ] ]
Solution In Java
Solution 1
public static int[] twoNumberSum(int[] array, int targetSum) {
for(int i=0;i<array.length;i++){
int first=array[i];
for(int j=i+1;j<array.length;j++){
int second=array[j];
if(first+second==targetSum){
return new int[]{first,second};
}
}
}
return new int[0];
}
Solution 2
public static int[] twoNumberSum(int[] array, int targetSum) {
Set<Integer> nums=new HashSet<Integer>();
for(int num:array){
int pmatch=targetSum-num;
if(nums.contains(pmatch)){
return new int[]{pmatch,num};
}else{
nums.add(num);
}
}
return new int[0];
}
Solution 3
public static int[] twoNumberSum(int[] array, int targetSum) {
Arrays.sort(array);
int left=0;
int right=array.length-1;
while(left<right){
int currentSum=array[left]+array[right];
if(currentSum==targetSum){
return new int[]{array[left],array[right]};
}else if(currentSum<targetSum){
left++;
}else if(currentSum>targetSum){
right--;
}
}
return new int[0];
}
function findPairOfNumbers(arr, targetSum) {
var low = 0, high = arr.length - 1, sum, result = [];
while(low < high) {
sum = arr[low] + arr[high];
if(sum < targetSum)
low++;
else if(sum > targetSum)
high--;
else if(sum === targetSum) {
result.push({val1: arr[low], val2: arr[high]});
high--;
}
}
return (result || false);
}
var pairs = findPairOfNumbers([1,2,3,4,4,5], 8);
if(pairs.length) {
console.log(pairs);
} else {
console.log("No pair of numbers found that sums to " + 8);
}
Simple Solution would be in javascript is:
var arr = [7,5,10,-5,9,14,45,77,5,3];
var arrLen = arr.length;
var sum = 15;
function findSumOfArrayInGiven (arr, arrLen, sum){
var left = 0;
var right = arrLen - 1;
// Sort Array in Ascending Order
arr = arr.sort(function(a, b) {
return a - b;
})
// Iterate Over
while(left < right){
if(arr[left] + arr[right] === sum){
return {
res : true,
matchNum: arr[left] + ' + ' + arr[right]
};
}else if(arr[left] + arr[right] < sum){
left++;
}else{
right--;
}
}
return 0;
}
var resp = findSumOfArrayInGiven (arr, arrLen, sum);
// Display Desired output
if(resp.res === true){
console.log('Matching Numbers are: ' + resp.matchNum +' = '+ sum);
}else{
console.log('There are no matching numbers of given sum');
}
Runtime test JSBin: https://jsbin.com/vuhitudebi/edit?js,console
Runtime test JSFiddle: https://jsfiddle.net/arbaazshaikh919/de0amjxt/4/
function sumOfTwo(array, sumNumber) {
for (i of array) {
for (j of array) {
if (i + j === sumNumber) {
console.log([i, j])
}
}
}
}
sumOfTwo([1, 2, 3], 4)
function twoSum(args , total) {
let obj = [];
let a = args.length;
for(let i = 0 ; i < a ; i++){
for(let j = 0; j < a ; j++){
if(args[i] + args[j] == total) {
obj.push([args[i] , args[j]])
}
}
}
console.log(obj)}
twoSum([10,20,10,40,50,60,70,30],60);
/* */
I am trying to implement heapsort in Javascript, but there is a undefined element at array.length - 2 and the element at index 0 is unsorted.
Here is the code:
var heapSort = function(array) {
var swap = function(array, firstIndex, secondIndex) {
var temp = array[firstIndex];
array[firstIndex] = array[secondIndex];
array[secondIndex] = temp;
};
var maxHeap = function(array, i) {
var l = 2 * i;
var r = l + 1;
var largest;
if (l <= array.heapSize && array[l] > array[i]) {
largest = l;
} else {
largest = i;
}
if (r <= array.heapSize && array[r] > array[largest]) {
largest = r;
}
if (largest != i) {
swap(array, i, largest);
maxHeap(array, largest);
}
};
var buildHeap = function(array) {
array.heapSize = array.length;
for (var i = Math.floor(array.length / 2); i >= 1; i--) {
maxHeap(array, i);
}
};
buildHeap(array);
for (var i = array.length; i >= 2; i--) {
swap(array, 1, i);
array.heapSize--;
maxHeap(array, 1);
}
};
var a = [55, 67, 10, 34, 25, 523, 1, -2];
heapSort(a);
document.getElementById("getHeapSort").innerHTML = a;
* {
font-family: Arial, sans-serif;
}
<p id="getHeapSort"></p>
I figured that array[i] == undefined when i = array.length. I tried fixing this (setting i = array.length - 1), but the array came out in an entirely different order. I also figured that 0 was never swapped because i is always greater than 0. Again, I tried, and the array came out in a entirely different order.
You were using 1-based indexing instead of 0-based indexing in JavaScript. I also added a trace for your convenience.
Try this:
var heapSort = function(array) {
var swap = function(array, firstIndex, secondIndex) {
var temp = array[firstIndex];
array[firstIndex] = array[secondIndex];
array[secondIndex] = temp;
};
var maxHeap = function(array, i) {
var l = 2 * i;
var r = l + 1;
var largest;
if (l < array.heapSize && array[l] > array[i]) {
largest = l;
} else {
largest = i;
}
if (r < array.heapSize && array[r] > array[largest]) {
largest = r;
}
if (largest != i) {
swap(array, i, largest);
maxHeap(array, largest);
}
};
var buildHeap = function(array) {
array.heapSize = array.length;
for (var i = Math.floor(array.length / 2); i >= 0; i--) {
maxHeap(array, i);
}
};
buildHeap(array);
for (var i = array.length-1; i >= 1; i--) {
swap(array, 0, i);
array.heapSize--;
maxHeap(array, 0);
document.getElementById("getHeapSort").innerHTML = document.getElementById("getHeapSort").innerHTML + a + "<br>";
}
};
var a = [55, 67, 10, 34, 25, 523, 1, -2];
document.getElementById("getHeapSort").innerHTML = a + "<br>";
heapSort(a);
Here is a JFiddle: http://jsfiddle.net/mbL5enL5/1/