LeetCode——052

/*

Follow up for N-Queens problem.

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



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*/

/*

解题思路：

跟上一个题很相似，甚至比上一个题目还要简单，只要求统计否和要求的个数，不需要记录结果

*/

class Solution {
public:
int totalNQueens(int n) {

string s(n,'.');

vector<string> vec(n,s);
int res=0;
dfs(0,vec,res);
return res;
}

void  dfs(int cur,vector<string>&vec,int&res){

if(cur==vec.size()){
++res;
return ;
}
for(int i=0;i<vec.size();i++){
if(isvalid(cur,i,vec)){
vec[cur][i]='Q';
dfs(cur+1,vec,res);
vec[cur][i]='.';
}
}

}

bool isvalid(int row,int col, vector<string>vec){

for(int i=0;i<row;i++){
for(int j=0;j<vec.size();j++){
if(vec[i][j]=='Q'){
if(j==col||(abs(i-row))==(abs(j-col)))return false;
}
}
}

return true;
}

};