LeetCode 题解（105）: N-Queens II

来源：互联网发布：看图软件mac 编辑：程序博客网时间：2024/05/21 17:33

题目：

Follow up for N-Queens problem.

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

题解：

和N-Queen I是一道题的两种问法。

C++版：

class Solution {private:    int results = 0; public:    int totalNQueens(int n) {        if(n == 0)            return results;        vector<int> location(n, -1);        trace(location, 0, n);        return results;    }        void trace(vector<int>& location, int level, int n) {        if(level == n) {            results++;            return;        }        for(int i = 0; i < n; i++) {            if(isValid(location, level, i)) {                location[level] = i;                trace(location, level + 1, n);                location[level] = -1;            }        }    }        bool isValid(vector<int>& location, int row, int col) {        for(int i = 0; i < row; i++) {            if(location[i] == col || abs(row - i) == abs(location[i] - col))                return false;        }        return true;    }};

Java版：

public class Solution {    private int results = 0;    public int totalNQueens(int n) {        if(n == 0)            return results;        int[] location = new int[n];        for(int i = 0; i < n; i++)            location[i] = -1;        trace(location, n, 0);        return results;    }        private void trace(int[] location, int n, int level) {        if(level == n) {            results++;            return;        }        for(int i = 0; i < n; i++) {            if(isValid(location, level, i)) {                location[level] = i;                trace(location, n, level + 1);                location[level] = -1;            }        }    }        private boolean isValid(int[] location, int row, int col) {        for(int i = 0; i < row; i++) {            if(location[i] == col || Math.abs(row - i) == Math.abs(location[i] - col))                return false;        }        return true;    }}

Python版：

class Solution:    # @return a list of lists of string    def totalNQueens(self, n):        #results = 0        if n == 0:            return 0        location = [-1 for i in range(n)]        results = [0]        def trace(location, n, level):            if level == n:                results[0] += 1                return            for i in range(n):                if isValid(location, level, i):                    location[level] = i                    trace(location, n, level+1)                    location[level] = -1        def isValid(location, row, col):            for i in range(row):                if location[i] == col or abs(row - i) == abs(location[i] - col):                    return False            return True        trace(location, n, 0)        return results[0]

0 0