八皇后问题

简单的dfs，非最优解，胜在思路清晰

class Solution {
    int res = 0;
    public int totalNQueens(int n) {
        boolean[][] grid = new boolean[n][n];
        dfs(grid,0);
        return res;
    }
    
    public void dfs(boolean[][] grid,int row){
        if(row == grid.length){
            ++res;
            return;
        }
        //遍历每一行
        for(int i=0 ; i<grid.length ; i++){
            if(isValid(grid,row,i)){
                grid[row][i] = true;
                //递归判断下一行
                dfs(grid,row+1);
                grid[row][i] = false;
            }
        }
    }
    int[][] dirs = {{1,0},{1,1},{1,-1},{0,-1},{0,1},{-1,-1},{-1,0},{-1,1}};
    //判断该格是否可以放置棋子
    public boolean isValid(boolean[][] grid,int x,int y){
        int n = grid.length;
        
        for(int[] dir : dirs){
            int i=x;
            int j=y;
            while(i>=0 && j>=0 && i<n && j<n){                
                if(grid[i][j]){
                    return false;
                }
                i+=dir[0];
                j+=dir[1];
            }
        }
        return true;
    }
}

来源：https://blog.csdn.net/weixin_44601714/article/details/102732582