[Function add]

1. Add leetcode solutions using C++.

Author: Seanforfun

leetcode/37. Sudoku Solver.md

@@ -118,4 +118,40 @@ class Solution {
 			return true;
 		}
 	}
+	```
+
+### C++ Version
+* Method 1: backtrace
+	```objectivec
+	class Solution {
+	private:
+		bool dfs(vector<vector<char>>& board, int i_start, int j_start){
+			for(int i = 0; i < 9; ++i, j_start = 0){
+				for(int j = 0; j < 9; ++j){
+					if(board[i][j] != '.') continue;
+					for(char c = '1'; c <= '9'; ++c){
+						if(check(board, i, j, c)){
+							board[i][j] = c;
+							if(dfs(board, i, j + 1)) return true;
+							board[i][j] = '.';
+						}
+					}
+					return false;
+				}
+			}
+			return true;
+		}
+		bool check(vector<vector<char>>& board, int row, int col, char c){
+			for(int i = 0; i < 9; i++){
+				if(board[row][i] == c) return false;
+				if(board[i][col] == c) return false;
+				if(board[3 * (row / 3) + i / 3][3 * (col / 3) + i % 3] == c) return false;
+			}
+			return true;
+		}
+	public:
+		void solveSudoku(vector<vector<char>>& board) {
+			dfs(board, 0, 0);
+		}
+	};
 	```

leetcode/51. N-Queens.md

@@ -164,4 +164,45 @@ class Solution {
         return true;
     }
 }
-```
+```
+
+### C++ Version
+* Method 1: dfs
+	```objectivec
+	class Solution {
+	private:
+		vector<vector<string>> res_;
+		bool check(vector<string>& board, int row, int col, int n){
+			for(int i = 0; i < n; ++i){
+				if(board[row][i] == 'Q') return false;
+				if(board[i][col] == 'Q') return false;            
+			}
+			int tx = row, ty = col;
+			while(tx >= 0 && ty >= 0) if(board[tx--][ty--] == 'Q') return false;
+			tx = row; ty = col;
+			while(tx >= 0 && ty < n) if(board[tx--][ty++] == 'Q') return false;
+			return true;
+		}
+		void dfs(int row, vector<string>& board, int n){
+			if(row == n) res_.emplace_back(board);
+			else{
+				for(int i = 0; i < n; ++i){
+					if(check(board, row, i, n)){
+						board[row][i] = 'Q';
+						dfs(row + 1, board, n);
+						board[row][i] = '.';
+					}
+				}
+			}
+		}
+	public:
+		vector<vector<string>> solveNQueens(int n) {
+			res_ = vector<vector<string>>();
+			string line = "";
+			for(int i = 0; i < n; ++i) line += ".";
+			vector<string> temp(n, line);
+			dfs(0, temp, n);
+			return res_;
+		}
+	};
+	```

leetcode/52. N-Queens II.md

@@ -147,3 +147,43 @@ class Solution {
       }
   }
   ```
+
+### C++ Version
+* Method 1: backtrace
+	```objectivec
+	class Solution {
+	private:
+		int res_;
+		bool check(vector<string>& board, int row, int col, int n){
+			for(int i = 0; i < n; ++i){
+				if(board[row][i] == 'Q') return false;
+				if(board[i][col] == 'Q') return false;
+			}
+			int tx = row, ty = col;
+			while(tx >= 0 && ty >= 0) if(board[tx--][ty--] == 'Q') return false;
+			while(row >= 0 && col < n) if(board[row--][col++] == 'Q') return false;
+			return true;
+		}
+		void dfs(vector<string>& board, int row, int n){
+			if(row == n) res_++;
+			else{
+				for(int i = 0; i < n; ++i){
+					if(check(board, row, i, n)){
+						board[row][i] = 'Q';
+						dfs(board, row + 1, n);
+						board[row][i] = '.';
+					}
+				}
+			}
+		}
+	public:
+		int totalNQueens(int n) {
+			res_ = 0;
+			string line = "";
+			for(int i = 0; i < n; ++i) line += ".";
+			vector<string> temp(n, line);
+			dfs(temp, 0, n);
+			return res_;
+		}
+	};
+	```