May 22, 2024 · May 19, 2024
diff --git a/java/0052-n-queens-ii.java b/java/0052-n-queens-ii.java
 class Solution {
    int count = 0;

    public int totalNQueens(int n) {
        Set<Integer> colSet = new HashSet<>();
        Set<Integer> posDiagSet = new HashSet<>(); // (r + c)
        Set<Integer> negDiagSet = new HashSet<>(); // (r - c)
        backtrack(0, n, colSet, posDiagSet, negDiagSet);
        return count;
    }

    private void backtrack(
            int row,
            int n,
            Set<Integer> colSet,
            Set<Integer> posDiagSet,
            Set<Integer> negDiagSet) {
        if (row == n) {
            count += 1;
            return;
        }

        for (int col = 0; col < n; col++) {
            if (colSet.contains(col)
                    || posDiagSet.contains(row + col)
                    || negDiagSet.contains(row - col)) {
                continue;
            }
            colSet.add(col);
            posDiagSet.add(row + col);
            negDiagSet.add(row - col);
            backtrack(row + 1, n, colSet, posDiagSet, negDiagSet);
            colSet.remove(col);
            posDiagSet.remove(row + col);
            negDiagSet.remove(row - col);
        }
    }
 }
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,38 @@
		class Solution {
		int count = 0;

		public int totalNQueens(int n) {
		Set<Integer> colSet = new HashSet<>();
		Set<Integer> posDiagSet = new HashSet<>(); // (r + c)
		Set<Integer> negDiagSet = new HashSet<>(); // (r - c)
		backtrack(0, n, colSet, posDiagSet, negDiagSet);
		return count;
		}

		private void backtrack(
		int row,
		int n,
		Set<Integer> colSet,
		Set<Integer> posDiagSet,
		Set<Integer> negDiagSet) {
		if (row == n) {
		count += 1;
		return;
		}

		for (int col = 0; col < n; col++) {
		if (colSet.contains(col)
		\|\| posDiagSet.contains(row + col)
		\|\| negDiagSet.contains(row - col)) {
		continue;
		}
		colSet.add(col);
		posDiagSet.add(row + col);
		negDiagSet.add(row - col);
		backtrack(row + 1, n, colSet, posDiagSet, negDiagSet);
		colSet.remove(col);
		posDiagSet.remove(row + col);
		negDiagSet.remove(row - col);
		}
		}
		}