Follow up for N-Queens problem.

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

DFS

1 class Solution { 2 private: 3     int ret; 4     int a[100]; 5     bool canUse[100]; 6 public: 7     bool check(int y, int n) 8     { 9         for(int i = 0; i < n; i++)10             if (abs(i - n) == abs(y - a[i]))11                 return false;12         return true;13     }14     15     void solve(int dep, int maxDep)16     {17         if (dep == maxDep)18         {19             ret++;            20             return;21         }22         23         for(int i = 0; i < maxDep; i++)24             if (canUse[i] && check(i, dep))25             {26                 canUse[i] = false;27                 a[dep] = i;28                 solve(dep + 1, maxDep);29                 canUse[i] = true;             30             }31     }32     33     int totalNQueens(int n) {34         // Start typing your C/C++ solution below35         // DO NOT write int main() function36         ret = 0;37         memset(canUse, true, sizeof(canUse));38         solve(0, n);39         return ret;40     }41 };