Update 0130.被围绕的区域.md

problems/0130.被围绕的区域.md

@@ -563,7 +563,9 @@ function solve(board) {
 
 ### Go
 
-```dfs
+dfs:
+
+```go
 var DIRECTIONS = [4][2]int{{-1, 0}, {0, -1}, {1, 0}, {0, 1}}
 
 func solve(board [][]byte) {
@@ -613,6 +615,64 @@ func dfs(board [][]byte, i, j int) {
 }
 ```
 
+bfs:
+
+```go
+var DIRECTIONS = [4][2]int{{-1, 0}, {0, -1}, {1, 0}, {0, 1}}
+
+func solve(board [][]byte) {
+	rows, cols := len(board), len(board[0])
+	// 列
+	for i := 0; i < rows; i++ {
+		if board[i][0] == 'O' {
+			bfs(board, i, 0)
+		}
+		if board[i][cols-1] == 'O' {
+			bfs(board, i, cols-1)
+		}
+	}
+	// 行
+	for j := 0; j < cols; j++ {
+		if board[0][j] == 'O' {
+			bfs(board, 0, j)
+		}
+		if board[rows-1][j] == 'O' {
+			bfs(board, rows-1, j)
+		}
+	}
+
+	for _, r := range board {
+		for j, c := range r {
+			if c == 'A' {
+				r[j] = 'O'
+			}
+			if c == 'O' {
+				r[j] = 'X'
+			}
+		}
+	}
+}
+
+func bfs(board [][]byte, i, j int) {
+	queue := [][]int{{i, j}}
+	board[i][j] = 'A'
+	for len(queue) > 0 {
+		cur := queue[0]
+		queue = queue[1:]
+		for _, d := range DIRECTIONS {
+			x, y := cur[0]+d[0], cur[1]+d[1]
+			if x < 0 || x >= len(board) || y < 0 || y >= len(board[0]) {
+				continue
+			}
+			if board[x][y] == 'O' {
+				board[x][y] = 'A'
+				queue = append(queue, []int{x, y})
+			}
+		}
+	}
+}
+```
+
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