Flip String to Monotone Increasing LeetCode solution in JavaScript

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function getPrefixSumArray(s) {
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  const prefixSumOfOnes = Array(s.length).fill(0);
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  let currentSum = 0;
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  for (let x = 0; x < s.length; x++) {
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    if (s[x] === "1") currentSum++;
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    prefixSumOfOnes[x] = currentSum;
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  }
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  return prefixSumOfOnes;
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}
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var minFlipsMonoIncr = function (s) {
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  const prefixSumOfOnes = getPrefixSumArray(s);
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  let answer = prefixSumOfOnes[s.length - 1]; // Case where we want to change to '0000'
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  for (let x = 0; x < s.length; x++) {
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    const sizeOfRightHandSide = s.length - x;
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    let numChangesRequired = null;
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    if (x === 0) {
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      // Case where we want to change to '1111'
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      const numOfOnesToChangeToZero = 0;
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      const numOfOnesOnRightHandSide = prefixSumOfOnes[s.length - 1];
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      const numOfZerosToChangeToOne =
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        sizeOfRightHandSide - numOfOnesOnRightHandSide;
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      numChangesRequired = numOfOnesToChangeToZero + numOfZerosToChangeToOne;
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    } else {
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      // Cases like '0111', '0011', '0001'
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      const numOfOnesToChangeToZero = prefixSumOfOnes[x - 1];
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      const numOfOnesOnRightHandSide =
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        prefixSumOfOnes[s.length - 1] - prefixSumOfOnes[x - 1];
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      const numOfZerosToChangeToOne =
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        sizeOfRightHandSide - numOfOnesOnRightHandSide;
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      numChangesRequired = numOfOnesToChangeToZero + numOfZerosToChangeToOne;
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    }
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    answer = Math.min(answer, numChangesRequired);
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  }
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  return answer;
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};