[Leetcode]N-Queens II

Follow up for N-Queens problem.

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



class Solution {
public:
/*algorithm: DFS
*/
vector<int>getNextCandiates(vector<int>&solution,int n)
{
vector<int>result;
for(int i = 0; i < n;i++){
bool selected = true;
for(int k = 0;k < solution.size();k++){
if(i == solution[k] || //same column or same k=1/-1 (k=(y2-y1)/(x2-x1))
abs(i-solution[k])==abs((int)solution.size()-k)){
selected = false;
break;
}
}
if(selected)result.push_back(i);
}
return result;
}

void dfs(int n,int start,int &sum,vector<int>&solution){
if(start == n){ //find one solution,reach last line
sum++;
return;
}
vector<int>candiates = getNextCandiates(solution,n);
for(int k = 0;k < candiates.size();k++){
solution.push_back(candiates[k]);
dfs(n,start+1,sum,solution);
solution.pop_back();
}
}
int totalNQueens(int n) {
vector<int>solution;
int sum = 0;
dfs(n,0,sum,solution);
return sum;
}
};