Added day17 solution and rearranged codebase

Author: avidLearnerInProgress

30-days-of-june/01.invertTree.cpp renamed to 30-days-of-code-june/01.invertTree.cpp

@@ -0,0 +1,29 @@
+class Solution {
+public:
+    void solve(vector<vector<char>>& board) {
+        if (board.empty()) return;
+        int row = board.size(), col = board[0].size();
+        for (int i = 0; i < row; ++i) {
+            check(board, i, 0);             // first column
+            check(board, i, col - 1);       // last column
+        }
+        for (int j = 1; j < col - 1; ++j) {
+            check(board, 0, j);             // first row
+            check(board, row - 1, j);       // last row
+        }
+        for (int i = 0; i < row; ++i)
+            for (int j = 0; j < col; ++j)
+                if (board[i][j] == 'O') board[i][j] = 'X';
+                else if (board[i][j] == '1') board[i][j] = 'O';
+    }
+    
+    void check(vector<vector<char>>& board, int i, int j) {
+        if (board[i][j] == 'O') {
+            board[i][j] = '1';
+            if (i > 1) check(board, i - 1, j);
+            if (j > 1) check(board, i, j - 1);
+            if (i + 1 < board.size()) check(board, i + 1, j);
+            if (j + 1 < board[0].size()) check(board, i, j + 1);
+        }
+    }
+};