N-Queens II

Leetcode/CPP/52. N-Queens II.cpp

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+//problem link:https://leetcode.com/problems/n-queens-ii/
+//Time complexity : best and average case O(n*n)    
+//worst case:O(n!)
+class Solution {
+public:
+     bool issafe(vector<string> &board,int n,int row,int col)
+{
+    for(int i=0;i<col;i++)
+    {
+        if(board[row][i]=='Q')
+        {
+            return false;
+        }
+    }
+    for(int i=row,j=col; i>=0 && j>=0; i--,j--)
+    {
+        if(board[i][j]=='Q')
+        {
+            return false;
+        }
+    }
+    for(int i=row,j=col; i<n && j>=0; i++,j--)
+    {
+        if(board[i][j]=='Q')
+        {
+            return false;
+        }
+    }
+    return true;
+}
+void nqueen(vector<vector<string>> &ans,vector<string> &board,int n,int col)
+{
+    if(col==n)
+    {
+       ans.push_back(board);
+    }
+    for(int row=0;row<n;row++)
+    {
+        if(issafe(board,n,row,col))
+        {
+            board[row][col]='Q';
+            nqueen(ans,board,n,col+1);
+            board[row][col]='.';
+        }
+    }
+}
+    int totalNQueens(int n) {
+         vector<vector<string>>ans;
+        vector<string>board(n);
+        string s(n,'.');
+        for (int i = 0; i < n; i++)
+        {
+            board[i]=s;
+        }
+        nqueen(ans,board,n,0);
+        return ans.size();
+    }
+};