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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 waysToMakeFair = function (nums) {
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  let oddSum = 0;
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  let evenSum = 0;
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  let count = 0;
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  for (let i = 0; i < nums.length; i++) {
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    if (i % 2 === 0) {
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      evenSum += nums[i];
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    } else {
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      oddSum += nums[i];
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    }
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  }
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  for (let i = 0; i < nums.length; i++) {
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    if (i % 2 === 0) {
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      evenSum -= nums[i];
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      if (evenSum === oddSum) {
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        count++;
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      }
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      oddSum += nums[i];
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    } else {
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      oddSum -= nums[i];
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      if (evenSum === oddSum) {
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        count++;
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      }
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      evenSum += nums[i];
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    }
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  }
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  return count;
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};