leetcode:N-Queens 问题

 1 class Solution {
 2 public:
 3     int totalNQueens(int n) {
 4         int total = 0;
 5         vector<int> v(n,0);
 6         dfs(0,n,total,v);
 7         return total;
 8     }
 9 private:
10     bool isvalide(vector<int>& v,int x){
11         for(int i=0;i<x;i++){
12             if(v[i]==v[x] || abs(v[x]-v[i])==abs(x - i))
13                 return false;
14         }
15         return true;
16     }
17 
18     void dfs(int curr,int n,int& total,vector<int>& v){
19         if(curr == n) {
20             total++;
21             return;
22         }
23 
24         for(int i=0;i<n;i++){
25             v[curr] = i;
26             if(isvalide(v,curr)){
27                 dfs(curr+1,n,total,v);
28             }
29         }
30     }
31 };

 1 class Solution {
 2 public:
 3     vector<vector<string>> solveNQueens(int n) {
 4         vector<vector<string>> result;
 5         vector<int> v(n,-1);
 6         dfs(0,n,v,result);
 7         return result;
 8     }
 9     bool isValide(vector<int>& v,int curr){
10         for(int i=0;i< curr;i++){
11             if(v[i] == v[curr] || abs(v[curr]-v[i])==abs(curr-i))
12                 return false;
13         }
14         return true;
15     }
16     void dfs(int curr,int n,vector<int>& v,
17             vector<vector<string>>& result){
18         if(curr == n){
19             vector<string> temp;
20             for(int i=0;i<n;i++){
21                 string s(n,‘.‘);
22                 s[v[i]] = ‘Q‘;
23                 temp.push_back(s);
24             }
25             result.push_back(temp);
26             return;
27         }
28         for(int i=0;i<n;i++){
29             v[curr] = i;
30             if(isValide(v,curr)){
31                 dfs(curr+1, n, v,result);
32             }
33         }
34     }
35 };