Can Convert String in K Moves LeetCode solution in JavaScript

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/**
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 * @param {string} s
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 * @param {string} t
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 * @param {number} k
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 * @return {boolean}
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 */
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var canConvertString = function (s, t, k) {
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  let res = true;
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  if (s.length === t.length) {
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    let tmp = [];
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    let countMap = new Map();
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    for (let i = 0; i < s.length; i++) {
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      let n1 = s[i].charCodeAt();
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      let n2 = t[i].charCodeAt();
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      let r = n2 - n1;
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      if (r < 0) {
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        r += 26;
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      }
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      // exclude special case 0
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      if (r > 0) {
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        // Considering repeated letters, the unrepeated move should change to r + 26*n (n>=0)
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        // use hash table to count the same letter
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        if (!countMap.has(r)) {
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          // first time to move
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          countMap.set(r, 1);
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          tmp.push(r);
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        } else {
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          // n time to move, n means the count of the same letter
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          let c = countMap.get(r);
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          tmp.push(r + c * 26);
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          // update count
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          countMap.set(r, c + 1);
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        }
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      }
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    }
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    // check all possible move in range
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    for (let i = 0; i < tmp.length; i++) {
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      let t = tmp[i];
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      if (t > k) {
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        res = false;
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        break;
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      }
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    }
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  } else {
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    res = false;
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  }
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  return res;
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};