Update surrounded-regions.cpp

Author: kamyu104

C++/surrounded-regions.cpp

@@ -10,34 +10,42 @@ class Solution {
 
         queue<pair<int, int>> q;
         for (int i = 0; i < board.size(); ++i) {
-            q.emplace(i, 0);
-            q.emplace(i, board[0].size() - 1);
-        }
-        for (int j = 0; j < board[0].size(); ++j) {
-            q.emplace(0, j);
-            q.emplace(board.size() - 1, j);
+            if (board[i][0] == 'O') {
+                board[i][0] = 'V';
+                q.emplace(i, 0);
+            }
+            if (board[i][board[0].size() - 1] == 'O') {
+                board[i][board[0].size() - 1] = 'V';
+                q.emplace(i, board[0].size() - 1);
+            }
         }
 
+        for (int j = 1; j < board[0].size() - 1; ++j) {
+            if (board[0][j] == 'O') {
+                board[0][j] = 'V';
+                q.emplace(0, j);
+            }
+            if (board[board.size() - 1][j] == 'O') {
+                board[board.size() - 1][j] = 'V';
+                q.emplace(board.size() - 1, j);
+            }
+        }
         while (!q.empty()) {
             int i, j;
             tie(i, j) = q.front();
             q.pop();
-            if (board[i][j] == 'O' || board[i][j] == 'V') {
-                board[i][j] = 'V';
-                const vector<pair<int, int>> directions{{0, -1}, {0, 1},
-                                                        {-1, 0}, {1, 0}};
-                for (const auto& d : directions) {
-                    const int x = i + d.first, y = j + d.second;
-                    if (0 <= x  && x < board.size() &&
-                        0 <= y && y < board[0].size() &&
-                        board[x][y] == 'O') {
-                        board[x][y] = 'V';
-                        q.emplace(x, y);
-                    }
+            static const vector<pair<int, int>> directions{{0, -1}, {0, 1},
+                                                           {-1, 0}, {1, 0}};
+            for (const auto& d : directions) {
+                const int x = i + d.first, y = j + d.second;
+                if (0 <= x && x < board.size() &&
+                    0 <= y && y < board[0].size() &&
+                    board[x][y] == 'O') {
+                    board[x][y] = 'V';
+                    q.emplace(x, y);
                 }
             }
         }
-
         for (int i = 0; i < board.size(); ++i) {
             for (int j = 0; j < board[0].size(); ++j) {
                 if (board[i][j] != 'V') {