solve number of island

Author: sora0319

number-of-islands/sora0319.java

@@ -0,0 +1,51 @@
+class Solution {
+    public int numIslands(char[][] grid) {
+        Queue<Pair> island = new LinkedList<>();
+        int N = grid.length;
+        int M = grid[0].length;
+        boolean[][] visited = new boolean[N][M];
+        int count = 0;
+
+        for(int i = 0; i < N; i++){
+            for(int j = 0; j < M; j++){
+                if(!visited[i][j] && grid[i][j] == '1'){
+                    island.offer(new Pair(i, j));
+                    visited[i][j] = true;
+                    bfs(grid, visited, island);
+                    count++;
+                }
+            }
+        }
+        return count;
+    }
+    public void bfs(char[][] grid, boolean[][] visited, Queue<Pair> island){
+        int[] mx = {-1, 1, 0, 0};
+        int[] my = {0, 0, -1, 1};
+
+
+        while(!island.isEmpty()){
+            Pair p = island.poll();
+            for(int i = 0; i < 4; i++){
+                int nx = mx[i] + p.x;
+                int ny = my[i] + p.y;
+
+                if(nx < 0 || ny < 0||  nx >= grid.length || ny >= grid[0].length) continue;
+                if(visited[nx][ny] || grid[nx][ny] == '0') continue;
+
+                island.offer(new Pair(nx, ny));
+                visited[nx][ny] = true;
+            }
+
+        }
+    }
+
+    class Pair{
+        int x;
+        int y;
+        Pair(int x, int y){
+            this.x = x;
+            this.y = y;
+        }
+    }
+}
+