LeetCode:N-Queens II

N-Queens II

Follow up for N-Queens problem.

Now, instead outputting board configurations, return the total number of distinct solutions.

public class Solution {
    public int totalNQueens(int n) {
        // Start typing your Java solution below
        // DO NOT write main() function
        assert(n>0);
        return countSolution(1,new int[n]);
    }
    
    public int countSolution(int k, int[] pattern){
        int n= pattern.length;
        assert(k<=n);
        int res = 0;
        main:
        for(int i=0;i<n;i++){
            for(int j=0;j<k-1;j++){
                if(pattern[j]==i||Math.abs(j-k+1)==Math.abs(pattern[j]-i))
                continue main;
            }
            pattern[k-1]=i;
            if(k==n) return 1;
            else res+=countSolution(k+1,pattern);
        }
        return res;
    }
}