g0001_0100.s0051_n_queens.Solution.cs Maven / Gradle / Ivy

Go to download

Show more of this group Show more artifacts with this name
Show all versions of leetcode-in-all Show documentation

104 LeetCode algorithm problem solutions

There is a newer version: 1.8

namespace LeetCodeNet.G0001_0100.S0051_n_queens {

// #Hard #Top_100_Liked_Questions #Array #Backtracking #Big_O_Time_O(N!)_Space_O(N)
// #2024_01_04_Time_106_ms_(96.34%)_Space_54.6_MB_(5.79%)

public class Solution {
    public IList> SolveNQueens(int n) {
        return this.Backtrack(n, 0, (x, y) => false).ToList();
    }

    private IEnumerable> Backtrack(int boardSize, int y, Func check) {
        for (int x = 0; x < boardSize; x++) {
            if (check(x, y)) {
                continue;
            }
            string currentLine = $"{new string('.', x)}Q{new string('.', boardSize - x - 1)}";
            if (y == boardSize - 1) {
                yield return new List { currentLine };
                continue;
            }
            var results = this.Backtrack(boardSize, y + 1, (xx, yy) =>
                check(xx, yy) ||
                (xx == x) ||
                (yy == (y - x) + xx) ||
                (yy == (x + y) - xx)
            );
            foreach (var result in results) {
                result.Add(currentLine);
                yield return result;
            }
        }
    }
}
}