adds week7

Author: YeonguChoe

number-of-islands/yeonguchoe.cpp

@@ -0,0 +1,68 @@
+class Solution {
+public:
+    int numIslands(vector<vector<char>>& grid) {
+        int count = 0;
+
+        int row_size = grid.size();
+        int column_size = grid[0].size();
+
+        queue<pair<int, int>> q;
+
+        for (int i = 0; i < row_size; i++) {
+            for (int j = 0; j < column_size; j++) {
+                if (grid[i][j] == '1') {
+                    LookAround(i, j, grid, q, row_size, column_size);
+                    count += 1;
+                }
+            }
+        }
+        return count;
+    }
+
+    // BFS
+    void LookAround(int& x, int& y, vector<vector<char>>& grid,
+                    queue<pair<int, int>>& q, int& row_size, int& column_size) {
+        pair<int, int> center_location{x, y};
+        q.push(center_location);
+
+        grid[x][y] = '0';
+
+        while (!q.empty()) {
+            pair<int, int> selected_location = q.front();
+            q.pop();
+
+            int selected_x = selected_location.first;
+            int selected_y = selected_location.second;
+
+            // 선택된 cell에서 왼쪽
+            if (selected_x - 1 >= 0 &&
+                grid[selected_x - 1][selected_y] == '1') {
+                q.push({selected_x - 1, selected_y});
+                grid[selected_x - 1][selected_y] = '0';
+            }
+
+            // 선택된 cell에서 오른쪽
+            if (selected_x + 1 < row_size &&
+                grid[selected_x + 1][selected_y] == '1') {
+                q.push({selected_x + 1, selected_y});
+                grid[selected_x + 1][selected_y] = '0';
+            }
+
+            // 선택된 cell에서 위쪽
+            if (selected_y - 1 >= 0 &&
+                grid[selected_x][selected_y - 1] == '1') {
+                q.push({selected_x, selected_y - 1});
+                grid[selected_x][selected_y - 1] = '0';
+            }
+
+            // 선택된 cell에서 아래쪽
+            if (selected_y + 1 < column_size &&
+                grid[selected_x][selected_y + 1] == '1') {
+                q.push({selected_x, selected_y + 1});
+                grid[selected_x][selected_y + 1] = '0';
+            }
+        }
+    }
+    // 시간 복잡도: O(row*column)
+    // 공간 복잡도: O(row*column)
+};