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

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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****************************************************************/

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