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var waysToSplit = function (nums) {
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  const mod = 1000000007;
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  const lastIndex = nums.length - 2;
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  const total = nums.reduce((sum, num) => sum + num);
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  let midLeftPtr = -1;
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  let midRightPtr = -1;
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  let leftSum = 0;
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  let midLeftSum = 0;
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  let midRightSum = 0;
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  let numWaysToSplit = 0;
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  for (let leftPtr = 0; leftPtr < nums.length; leftPtr++) {
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    leftSum += nums[leftPtr];
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    midLeftSum -= nums[leftPtr];
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    midRightSum -= nums[leftPtr];
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    // find the first index that satisfies the middle sum
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    // being greater than or equal to the left sum
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    while (
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      midLeftPtr <= lastIndex &&
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      (midLeftPtr <= leftPtr || midLeftSum < leftSum)
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    ) {
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      midLeftPtr++;
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      midLeftSum += nums[midLeftPtr];
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    }
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    // find the first index that makes the middle sum greater than the right sum
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    while (
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      midRightPtr <= lastIndex &&
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      (midLeftPtr > midRightPtr || midRightSum <= total - midRightSum - leftSum)
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    ) {
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      midRightPtr++;
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      midRightSum += nums[midRightPtr];
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    }
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    numWaysToSplit = (numWaysToSplit + midRightPtr - midLeftPtr) % mod;
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  }
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  return numWaysToSplit;
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};