leetcode-51-N-Queens II

问题

题目：[leetcode-51]

思路

dfs注意剪枝。恢复状态。

代码

class Solution {public:    int totalNQueens(int n) {        vector<int> visited;        int ans = 0;        dfs( n, 0, visited, ans );        return ans;    }private:    void dfs( int n, int cur, vector<int>& visited, int& ans ){        if( cur == n ) ++ans;        else{            for(int k = 0; k < n; ++k){                if( valid(cur, k, visited) ){                    visited.push_back( k );                    dfs( n, cur+1, visited, ans );                    visited.pop_back();                }            }        }    }// dfs    bool valid( int x, int y, vector<int>& visited ){        int sz = visited.size();        for(int u = 0; u < sz; ++u){            int v = visited[u];            // same colume            if( y == v ) return false;            // same diag            if( abs(x-u) == abs(y-v) ) return false;        }        return true;    }// valid};