Swapping array Indices

Question

I am trying to find the maximum of a number by swapping two digits. I have written the correct logic and it is getting to the part where I need to swap however after the swap i return the result and it isn't swapping?

var maximumSwap = function(num) {
   let str = num.toString()
   let left = 0
   let right = 1

   while (left !== str.length) {
     if (parseInt(str[left]) < parseInt(str[right])) {
       console.log(str[left], str[right])
       let temp = str[left];
       str[left] = str[right];
       str[right] = temp;
       return str
     } else if (parseInt(str[left]) > parseInt(str[right])) {
       if (left === right) {
         left++
         right = left + 1
       } else if (left < right) {
         right++
       }
     }

   }
};

maximumSwap(2736)
// Input: 2736
// Output: 7236
// Explanation: Swap the number 2 and the number 7.

another_CS_guy · Answer 1 · 2020-08-17T03:34:11.643

1

String are immutable in JS. Even though you are changing characters at left and right position, it wont reflect in "str".

Use this link on how to replace characters: How do I replace a character at a particular index in JavaScript?

Also, your logic is incorrect, if the first position element is largest, loop will run infinite times.

edited Aug 17 '20 at 03:34

answered Aug 17 '20 at 03:29

another_CS_guy

682
6
7

score 0 · Answer 2 · answered Aug 17 '20 at 03:45

// u can convert the num to string array to exchange
const str = num.toString().split('')

there is an example

// Input: 2736
// Output: 7632
var maximumSwap = function(num) {
   let str = num.toString().split('')
   let left = 0
   let right = 1

   while (left < str.length - 1) {
     while(right < str.length) {
        if (parseInt(str[left]) < parseInt(str[right])) {
          // exchange
          [str[left], str[right]] = [str[right], str[left]]
        }
        right++
     }
     left++
     right = left
   }
   return str.join('')
};

Swapping array Indices

2 Answers2