【LeetCode】N-Queens II && 【九度】题目1254：N皇后问题

N-Queens II
Total Accepted: 2737 Total Submissions: 10408 My Submissions
Follow up for N-Queens problem.
Now, instead outputting board configurations, return the total number of distinct solutions.

这个其实比N-Queens要简单，只需要输出个数就可以。
BFS超时，DFS很快就过了，和九度题目1254：N皇后问题一样，也是DFS。
Java DFS AC

public class Solution {
    public int totalNQueens(int n) {
        if(n <= 0){
            return 0;
        }
        int []queen = new int[n + 1];
        count = 0;
        for(int i = 1; i < n+1 ; i++){
            queen[1] = i;
            dfs(queen,2,n);
        }
        return count;
    }
    public int count ;
    public void dfs(int queen[], int line, int n) {
        if(line == n+1){
            count ++;
            return;
        }
        for(int i = 1; i < n+1; i++){
            if(valid(line, i, queen)){
                queen[line] = i;
                dfs(queen ,line+1, n);
                queen[line] = 0;
            }
        }
    }
    public boolean valid(int row, int col, int []queen) {
        for (int i = 1; i < row; i++) {
            if (queen[i] != 0 && (queen[i] == col 
				|| Math.abs(i - row) == Math.abs(queen[i] - col)))  
                return false;  
        }
        return true;
    }
}

九度题目1254：N皇后问题
Java DFS AC

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.StreamTokenizer;
  
public class Main{
    /*
     * 1254
     */
    public static int count;
    public static void main(String[] args) throws Exception {
        StreamTokenizer st = new StreamTokenizer
			(new BufferedReader(new InputStreamReader(System.in)));
        while (st.nextToken() != StreamTokenizer.TT_EOF) {
            int n = (int) st.nval;
            count = 0;
            solveNQueens(n);
            System.out.println(count);
        }
    }
    public static void solveNQueens(int n) {
        if(n <= 0){
            return;
        }
        int []queen = new int[n + 1];
        for(int i = 1; i < n+1 ; i++){
            queen[1] = i;
            dfs(queen,2,n);
        }
    }
    public static void dfs(int queen[], int line, int n) {
        if(line == n+1){
            count++;
            return;
        }
        for(int i = 1; i < n+1; i++){
            if(valid(line, i, queen)){
                queen[line] = i;
                dfs(queen,line+1, n);
                queen[line] = 0;
            }
        }
    }
    public static boolean valid(int row, int col, int []queen) {
        for (int i = 1; i < row; i++) {
            if (queen[i] != 0 && (queen[i] == col 
				|| Math.abs(i - row) == Math.abs(queen[i] - col)))  
                return false;  
        }
        return true;
    }
}
  
/**************************************************************
    Problem: 1254
    User: wangzhenqing
    Language: Java
    Result: Accepted
    Time:2860 ms
    Memory:17600 kb
****************************************************************/