Arithmetic Slices II - Subsequence 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 numberOfArithmeticSlices = function (nums) {
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  let dp = new Array(nums.length);
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  for (let i = 0; i < nums.length; i++) {
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    dp[i] = new Map();
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  }
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  let ans = 0;
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  for (let j = 1; j < nums.length; j++) {
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    for (let i = 0; i < j; i++) {
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      let commonDifference = nums[j] - nums[i];
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      if (
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        commonDifference > Math.pow(2, 31) - 1 ||
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        commonDifference < -Math.pow(2, 31)
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      ) {
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        continue;
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      }
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      let apsEndingAtI = dp[i].get(commonDifference) || 0;
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      let apsEndingAtJ = dp[j].get(commonDifference) || 0;
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      dp[j].set(commonDifference, apsEndingAtI + apsEndingAtJ + 1);
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      ans += apsEndingAtI;
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    }
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  }
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  return ans;
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};