Merge pull request royalpranjal#30 from khannagautam/patch-3

Added solution for N Queens

Author: Sahil

Backtracking/N Queens

@@ -0,0 +1,50 @@
+vector<vector<string> >ans;
+int n;
+
+void recur(int ind, vector<int> pos)
+{
+    int i,j;
+    if(ind == n)
+    {
+       vector<string> valid;
+        for(i=0;i<n;i++)
+        {
+            string row = "";
+            for(j=0;j<n;j++)
+            {
+                if(j == pos[i])
+                    row += 'Q';
+                else
+                    row += '.';
+            }
+            valid.push_back(row);
+        }
+        ans.push_back(valid);
+    
+        return;
+    }
+    for(i = 0;i<n;i++)
+    {
+        bool flag = true;
+        for(j=0;j<pos.size();j++)
+        {
+            if(abs(ind-j) == abs(pos[j]-i) || i == pos[j])
+                flag = false;
+        }
+        if(!flag)
+            continue;
+        pos.push_back(i);
+        recur(ind+1,pos);
+        pos.pop_back();
+        //pos[ind] = -1;
+    }
+}
+vector<vector<string> > Solution::solveNQueens(int A) 
+{
+    ans.clear();
+    vector<int> pos;
+    int i;
+    n = A;
+    recur(0,pos);
+    return ans;
+}