N-Queens II

class Solution {
public:
    int totalNQueens(int n) {
        int count = 0;
        function<void(int,int,int,int)> dfs = [&](int row, int cols, int diag, int anti) {
            if (row == n) { ++count; return; }
            int avail = ~(cols | diag | anti) & ((1 << n) - 1);
            while (avail) {
                int bit = avail & -avail;       // lowest set bit
                avail ^= bit;
                dfs(row + 1, cols | bit, (diag | bit) << 1, (anti | bit) >> 1);
            }
        };
        dfs(0, 0, 0, 0);
        return count;
    }
};

func totalNQueens(n int) int {
    count := 0
    var dfs func(row, cols, diag, anti int)
    dfs = func(row, cols, diag, anti int) {
        if row == n {
            count++
            return
        }
        avail := ^(cols | diag | anti) & ((1 << n) - 1)
        for avail != 0 {
            bit := avail & -avail
            avail ^= bit
            dfs(row+1, cols|bit, (diag|bit)<<1, (anti|bit)>>1)
        }
    }
    dfs(0, 0, 0, 0)
    return count
}

class Solution:
    def totalNQueens(self, n: int) -> int:
        count = 0
        full = (1 << n) - 1

        def dfs(row: int, cols: int, diag: int, anti: int) -> None:
            nonlocal count
            if row == n:
                count += 1
                return
            avail = ~(cols | diag | anti) & full
            while avail:
                bit = avail & -avail
                avail ^= bit
                dfs(row + 1, cols | bit, ((diag | bit) << 1) & full, (anti | bit) >> 1)

        dfs(0, 0, 0, 0)
        return count

function totalNQueens(n) {
    let count = 0;
    const full = (1 << n) - 1;
    const dfs = (row, cols, diag, anti) => {
        if (row === n) { count++; return; }
        let avail = ~(cols | diag | anti) & full;
        while (avail) {
            const bit = avail & -avail;
            avail ^= bit;
            dfs(row + 1, cols | bit, ((diag | bit) << 1) & full, (anti | bit) >> 1);
        }
    };
    dfs(0, 0, 0, 0);
    return count;
}

class Solution {
    private int count;
    private int n;
    private int full;

    public int totalNQueens(int n) {
        this.n = n;
        this.full = (1 << n) - 1;
        this.count = 0;
        dfs(0, 0, 0, 0);
        return count;
    }

    private void dfs(int row, int cols, int diag, int anti) {
        if (row == n) { count++; return; }
        int avail = ~(cols | diag | anti) & full;
        while (avail != 0) {
            int bit = avail & -avail;
            avail ^= bit;
            dfs(row + 1, cols | bit, ((diag | bit) << 1) & full, (anti | bit) >> 1);
        }
    }
}

function totalNQueens(n: number): number {
    let count = 0;
    const full = (1 << n) - 1;
    const dfs = (row: number, cols: number, diag: number, anti: number): void => {
        if (row === n) { count++; return; }
        let avail = ~(cols | diag | anti) & full;
        while (avail) {
            const bit = avail & -avail;
            avail ^= bit;
            dfs(row + 1, cols | bit, ((diag | bit) << 1) & full, (anti | bit) >> 1);
        }
    };
    dfs(0, 0, 0, 0);
    return count;
}