Maximum Sum of Two Non-Overlapping Subarrays LeetCode solution in JavaScript

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var maxSumTwoNoOverlap = function (nums, firstLen, secondLen) {
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  function helper(arr, x, y) {
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    const n = arr.length;
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    let sum = 0;
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    const dp1 = []; // store left x sum
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    const dp2 = []; // store right y sum
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    for (let i = 0; i < n; i++) {
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      if (i < x) {
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        sum += arr[i];
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        dp1[i] = sum;
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      } else {
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        sum += arr[i] - arr[i - x];
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        dp1[i] = Math.max(dp1[i - 1], sum);
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      }
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    }
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    sum = 0;
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    for (let i = n - 1; i >= 0; i--) {
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      if (i >= n - y) {
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        sum += arr[i];
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        dp2[i] = sum;
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      } else {
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        sum += arr[i] - arr[i + y];
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        dp2[i] = Math.max(dp2[i + 1], sum);
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      }
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    }
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    let max = -Infinity;
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    for (let i = x - 1; i < n - y; i++) {
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      max = Math.max(max, dp1[i] + dp2[i + 1]);
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    }
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    return max;
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  }
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  return Math.max(
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    helper(nums, firstLen, secondLen),
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    helper(nums, secondLen, firstLen)
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  );
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};