Minimum Absolute Difference Queries LeetCode solution in JavaScript

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var minDifference = function (nums, queries) {
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  const qlen = queries.length,
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    len = nums.length;
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  const res = new Array(qlen).fill(-1);
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  const prefix = [];
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  for (let i = 0; i <= len; i++) {
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    if (i == 0) prefix[i] = new Array(101).fill(0);
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    else {
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      prefix[i] = Array.from(prefix[i - 1]);
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      prefix[i][nums[i - 1]]++;
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    }
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  }
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  for (let k = 0; k < qlen; k++) {
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    const [l, r] = queries[k];
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    const left = prefix[l],
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      right = prefix[r + 1];
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    let prev = -1,
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      ans = Infinity;
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    for (let i = 1; i <= 100; i++) {
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      const diff = right[i] - left[i];
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      if (diff == 0) continue;
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      if (prev != -1) {
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        ans = Math.min(ans, i - prev);
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      }
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      prev = i;
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    }
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    if (ans != Infinity) {
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      res[k] = ans;
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    }
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  }
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  return res;
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};