Merge pull request #33 from akshaysoni10/LeetCode-Solution

N-Queen solution updated

Author: kishanrajput23

Convert_Sorted_Array_To_BST.cpp

@@ -0,0 +1,20 @@
+class Solution {
+public:
+    TreeNode* solve(vector<int> &nums, int start, int end){
+        //base case
+        if(start > end){
+            return NULL;
+        }
+        
+        int mid = (start + end)/2;
+        TreeNode* temp = new TreeNode(nums[mid]);
+        
+        temp -> left = solve(nums, start, mid-1);
+        temp -> right = solve(nums, mid+1, end);
+        return temp;
+        }
+    
+    TreeNode* sortedArrayToBST(vector<int>& nums) {
+        return solve(nums, 0, nums.size()-1);    
+    }
+};

Intersection_of_Two_LL.cpp

@@ -0,0 +1,22 @@
+class Solution {
+public:
+    ListNode *getIntersectionNode(ListNode *headA, ListNode *headB) {
+        ListNode* a = headA, *b = headB;
+        while(a != b){
+            if(a == NULL){
+                a = headB;
+            }
+            else{
+                a = a -> next;
+            }
+            
+            if(b == NULL){
+                b = headA;
+            }
+            else{
+                b = b -> next;
+            }
+        }
+        return a;
+    }
+};

N_Queen.cpp

@@ -0,0 +1,36 @@
+class Solution {
+public:
+    void solve(int col, vector<string> &board, vector<vector<string>> &ans, vector<int> &leftRow, vector<int> &upperDiagonal, vector<int> &lowerDiagonal, int n){
+        //base case
+        if(col == n){
+            ans.push_back(board);
+            return;
+        }
+        
+        for(int row=0; row<n; row++){
+            if(leftRow[row] == 0 && lowerDiagonal[row + col] == 0 && upperDiagonal[n-1 + col - row] == 0){
+                board[row][col] = 'Q';
+                leftRow[row] = 1;
+                lowerDiagonal[row + col] = 1;
+                upperDiagonal[n-1 + col - row] = 1;
+                solve(col + 1, board, ans, leftRow, upperDiagonal, lowerDiagonal, n);
+                board[row][col] = '.';
+                leftRow[row] = 0;
+                lowerDiagonal[row + col] = 0;
+                upperDiagonal[n-1 + col - row] = 0;
+            }
+        }
+    }
+    
+    vector<vector<string>> solveNQueens(int n) {
+        vector<vector<string>> ans;
+        vector<string> board(n);
+        string s(n, '.');
+        for(int i=0; i<n; i++){
+            board[i] = s;
+        }
+        vector<int> leftRow(n, 0), upperDiagonal(2 * n - 1, 0), lowerDiagonal(2 * n - 1, 0);
+        solve(0, board, ans, leftRow, upperDiagonal, lowerDiagonal, n);
+        return ans;
+    }
+};