week9 mission - Number of Islands

Author: dev-jonghoonpark

number-of-islands/dev-jonghoonpark.md

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+- 문제: https://leetcode.com/problems/number-of-islands/
+- 풀이: https://algorithm.jonghoonpark.com/2024/03/31/leetcode-200
+
+```java
+class Solution {
+    public int numIslands(char[][] grid) {
+        int w = grid.length;
+        int h = grid[0].length;
+
+        int count = 0;
+        for (int i = 0; i < w; i++) {
+            for (int j = 0; j < h; j++) {
+                if (grid[i][j] == '1') {
+                    dfs(grid, i,j);
+                    count++;
+                }
+            }
+        }
+        return count;
+    }
+
+    public void dfs(char[][] grid, int i, int j) {
+        if(i < 0 || i >= w || j < 0 || j >= h || grid[i][j] == '0') {
+            return;
+        }
+
+        grid[i][j] = '0';
+
+        dfs(grid, i-1, j);
+        dfs(grid, i, j-1);
+        dfs(grid, i+1, j);
+        dfs(grid, i, j+1);
+    }
+}
+```
+
+## TC, SC
+
+코드에 정의한 대로 grid의 길이를 `w`, grid[0]의 길이를 `h`로 정의했을 때,
+이 코드의 시간 복잡도는 O(w \* h), 공간 복잡도는 O(w \* h) 이다.