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130. Surrounded Regions.go
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130. Surrounded Regions.go
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package leetcode
import (
"github.com/halfrost/LeetCode-Go/template"
)
var dir = [][]int{
{-1, 0},
{0, 1},
{1, 0},
{0, -1},
}
// 解法一 并查集
func solve(board [][]byte) {
if len(board) == 0 {
return
}
m, n := len(board[0]), len(board)
uf := template.UnionFind{}
uf.Init(n*m + 1) // 特意多一个特殊点用来标记
for i := 0; i < n; i++ {
for j := 0; j < m; j++ {
if (i == 0 || i == n-1 || j == 0 || j == m-1) && board[i][j] == 'O' { //棋盘边缘上的 'O' 点
uf.Union(i*m+j, n*m)
} else if board[i][j] == 'O' { //棋盘非边缘上的内部的 'O' 点
if board[i-1][j] == 'O' {
uf.Union(i*m+j, (i-1)*m+j)
}
if board[i+1][j] == 'O' {
uf.Union(i*m+j, (i+1)*m+j)
}
if board[i][j-1] == 'O' {
uf.Union(i*m+j, i*m+j-1)
}
if board[i][j+1] == 'O' {
uf.Union(i*m+j, i*m+j+1)
}
}
}
}
for i := 0; i < n; i++ {
for j := 0; j < m; j++ {
if uf.Find(i*m+j) != uf.Find(n*m) {
board[i][j] = 'X'
}
}
}
}
// 解法二 DFS
func solve1(board [][]byte) {
for i := range board {
for j := range board[i] {
if i == 0 || i == len(board)-1 || j == 0 || j == len(board[i])-1 {
if board[i][j] == 'O' {
dfs130(i, j, board)
}
}
}
}
for i := range board {
for j := range board[i] {
if board[i][j] == '*' {
board[i][j] = 'O'
} else if board[i][j] == 'O' {
board[i][j] = 'X'
}
}
}
}
func dfs130(i, j int, board [][]byte) {
if i < 0 || i > len(board)-1 || j < 0 || j > len(board[i])-1 {
return
}
if board[i][j] == 'O' {
board[i][j] = '*'
for k := 0; k < 4; k++ {
dfs130(i+dir[k][0], j+dir[k][1], board)
}
}
}