Count Special Quadruplets LeetCode solution in JavaScript

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/**
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 * @param {number[]} nums
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 * @return {number}
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 */
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var countQuadruplets = function (nums) {
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  const map = new Map();
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  for (let i = 0; i < nums.length; i++) {
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    let n = nums[i];
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    if (map.has(n)) {
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      let t = map.get(n);
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      t.push(i);
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      map.set(n, t);
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    } else {
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      map.set(n, [i]);
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    }
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  }
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  let count = 0;
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  for (let a = 0; a < nums.length - 3; a++) {
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    for (let b = a + 1; b < nums.length - 2; b++) {
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      for (let c = b + 1; c < nums.length - 1; c++) {
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        let sum = nums[a] + nums[b] + nums[c];
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        let indexes = map.get(sum) || [];
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        //t is the d index that might exist
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        let t = c + 1;
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        let low = 0;
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        let high = indexes.length - 1;
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        let ans = -1;
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        while (low <= high) {
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          let mid = low + Math.floor((high - low) / 2);
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          if (indexes[mid] === t) {
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            ans = mid;
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            break;
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          }
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          if (indexes[mid] < t) {
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            low = mid + 1;
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          } else {
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            ans = mid;
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            high = mid - 1;
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          }
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        }
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        if (ans !== -1) {
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          count += indexes.length - ans;
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        }
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      }
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    }
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  }
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  return count;
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};