题目：

题解：

func totalNQueens(n int) (ans int) {
    columns := make([]bool, n)        // 列上是否有皇后
    diagonals1 := make([]bool, 2*n-1) // 左上到右下是否有皇后
    diagonals2 := make([]bool, 2*n-1) // 右上到左下是否有皇后
    var backtrack func(int)
    backtrack = func(row int) {
        if row == n {
            ans++
            return
        }
        for col, hasQueen := range columns {
            d1, d2 := row+n-1-col, row+col
            if hasQueen || diagonals1[d1] || diagonals2[d2] {
                continue
            }
            columns[col] = true
            diagonals1[d1] = true
            diagonals2[d2] = true
            backtrack(row + 1)
            columns[col] = false
            diagonals1[d1] = false
            diagonals2[d2] = false
        }
    }
    backtrack(0)
    return
}