Minimum Deletions to Make String Balanced LeetCode solution in JavaScript

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var minimumDeletions = function (s) {
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  const dpA = [];
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  let counter = 0;
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  for (let i = 0; i < s.length; i++) {
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    dpA[i] = counter;
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    if (s[i] === "b") {
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      counter++;
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    }
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  }
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  counter = 0;
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  const dpB = [];
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  for (let i = s.length - 1; i >= 0; i--) {
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    dpB[i] = counter;
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    if (s[i] === "a") {
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      counter++;
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    }
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  }
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  let minDelete = s.length;
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  for (let i = 0; i < s.length; i++) {
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    minDelete = Math.min(minDelete, dpA[i] + dpB[i]);
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  }
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  return minDelete;
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};