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//解法一 dfs
func numIslands(grid [][]byte) int {
ret := 0
if len(grid) == 0 {
return ret
}
m, n := len(grid), len(grid[0])
for i := 0; i < m; i++ {
for j := 0; j < n; j++ {
if grid[i][j] == '1' {
dfs(grid, i, j)
ret++
}
}
}
return ret
}
func dfs(grid [][]byte, i int, j int) {
if i < 0 || i >= len(grid) || j < 0 || j >= len(grid[0]) {
return
}
if grid[i][j] == '0' {
return
}
grid[i][j] = '0'
dfs(grid, i-1, j)
dfs(grid, i+1, j)
dfs(grid, i, j-1)
dfs(grid, i, j+1)
}
//解法二 查并集
var match []int
func find(x int) int {
if x != match[x] {
match[x] = find(match[x])
}
return match[x]
}
func numIslands(grid [][]byte) int {
m := len(grid)
if m == 0 {
return 0
}
n := len(grid[0])
match = make([]int, m*n)
for i := 0; i < m*n; i++ {
match[i] = i
}
for i := 0; i < m; i++ {
for j := 0; j < n; j++ {
x := i*n + j // 当前坐标
if grid[i][j] == '0' {
match[x] = -1
continue
}
// 数字x和改行向上的数字比较
if i != 0 && grid[i-1][j] == '1' {
y := (i-1)*n + j
match[find(x)] = find(y)
}
// 数字x和该列向左的数字比较
if j != 0 && grid[i][j-1] == '1' {
y := i*n + j - 1
match[find(x)] = find(y)
}
}
}
res := 0
mp := make(map[int]int)
for i := 0; i < m*n; i++ {
if match[i] == -1 {
continue
}
y := find(i)
if mp[y] != 1 {
res++
mp[y] = 1
}
}
return res
}
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