N-Queens II LeetCode solution in JavaScript

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/**
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 * @param {number} n
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 * @return {number}
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 */
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var totalNQueens = function (n) {
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  // Keep track of columns with queens
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  const cols = new Set();
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  // Keep track of positive slope diagonal by storing row number + column number
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  const posDiag = new Set();
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  // Keep track of negative slope diagonal by storing row number - column number
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  const negDiag = new Set();
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  // Count of valid boards
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  let count = 0;
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  const backtrack = function (r) {
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    // Base case to end recursion, we have traversed board and found valid position in each row
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    if (r === n) {
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      count += 1;
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      return;
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    }
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    // Loop through each column to see if you can place a queen
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    for (let c = 0; c < n; c++) {
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      // invalid position check, if position in set we cannot place queen here
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      if (cols.has(c) || posDiag.has(r + c) || negDiag.has(r - c)) continue;
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      // add new queen to sets
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      cols.add(c);
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      posDiag.add(r + c);
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      negDiag.add(r - c);
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      // backtrack
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      backtrack(r + 1);
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      // remove current position from sets because backtracking for this position is complete
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      cols.delete(c);
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      posDiag.delete(r + c);
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      negDiag.delete(r - c);
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    }
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  };
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  backtrack(0);
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  return count;
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};