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feat: add solutions to lc problem: No.1905.Count Sub Islands
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‎solution/1900-1999/1905.Count Sub Islands/README.md

+114-10
Original file line numberDiff line numberDiff line change
@@ -45,14 +45,16 @@ grid2 中标红的 1 区域是子岛屿，总共有 2 个子岛屿。
4545

4646
<!-- 这里可写通用的实现逻辑 -->
4747

48-
深度优先搜索。
48+
深度优先搜索，或者并查集。
4949

5050
<!-- tabs:start -->
5151

5252
### **Python3**
5353

5454
<!-- 这里可写当前语言的特殊实现逻辑 -->
5555

56+
DFS：
57+
5658
```python
5759
class Solution:
5860
def countSubIslands(self, grid1: List[List[int]], grid2: List[List[int]]) -> int:
@@ -75,10 +77,47 @@ class Solution:
7577
return count
7678
```
7779

80+
并查集：
81+
82+
```python
83+
class Solution:
84+
def countSubIslands(self, grid1: List[List[int]], grid2: List[List[int]]) -> int:
85+
m, n = len(grid1), len(grid1[0])
86+
p = list(range(m * n))
87+
88+
def find(x):
89+
if p[x] != x:
90+
p[x] = find(p[x])
91+
return p[x]
92+
93+
for i in range(m):
94+
for j in range(n):
95+
if grid2[i][j] == 1:
96+
idx = i * n + j
97+
if i < m - 1 and grid2[i + 1][j] == 1:
98+
p[find(idx)] = find((i + 1) * n + j)
99+
if j < n - 1 and grid2[i][j + 1] == 1:
100+
p[find(idx)] = find(i * n + j + 1)
101+
102+
s = [0] * (m * n)
103+
for i in range(m):
104+
for j in range(n):
105+
if grid2[i][j] == 1:
106+
s[find(i * n + j)] = 1
107+
for i in range(m):
108+
for j in range(n):
109+
root = find(i * n + j)
110+
if s[root] and grid1[i][j] == 0:
111+
s[root] = 0
112+
return sum(s)
113+
```
114+
78115
### **Java**
79116

80117
<!-- 这里可写当前语言的特殊实现逻辑 -->
81118

119+
DFS：
120+
82121
```java
83122
class Solution {
84123
private int[][] directions = {{0, 1}, {0, - 1}, {1, 0}, {-1, 0}};
@@ -113,6 +152,65 @@ class Solution {
113152
}
114153
```
115154

155+
并查集：
156+
157+
```java
158+
class Solution {
159+
private int[] p;
160+
161+
public int countSubIslands(int[][] grid1, int[][] grid2) {
162+
int m = grid2.length, n = grid2[0].length;
163+
p = new int[m * n];
164+
for (int i = 0; i < p.length; ++i) {
165+
p[i] = i;
166+
}
167+
for (int i = 0; i < m; ++i) {
168+
for (int j = 0; j < n; ++j) {
169+
if (grid2[i][j] == 1) {
170+
int idx = i * n + j;
171+
if (i < m - 1 && grid2[i + 1][j] == 1) {
172+
p[find(idx)] = find((i + 1) * n + j);
173+
}
174+
if (j < n - 1 && grid2[i][j + 1] == 1) {
175+
p[find(idx)] = find(i * n + j + 1);
176+
}
177+
}
178+
}
179+
}
180+
boolean[] s = new boolean[m * n];
181+
for (int i = 0; i < m; ++i) {
182+
for (int j = 0; j < n; ++j) {
183+
if (grid2[i][j] == 1) {
184+
s[find(i * n + j)] = true;
185+
}
186+
}
187+
}
188+
for (int i = 0; i < m; ++i) {
189+
for (int j = 0; j < n; ++j) {
190+
int root = find(i * n + j);
191+
if (s[root] && grid1[i][j] == 0) {
192+
s[root] = false;
193+
}
194+
}
195+
}
196+
int res = 0;
197+
for (boolean e : s) {
198+
if (e) {
199+
++res;
200+
}
201+
}
202+
return res;
203+
}
204+
205+
private int find(int x) {
206+
if (p[x] != x) {
207+
p[x] = find(p[x]);
208+
}
209+
return p[x];
210+
}
211+
}
212+
```
213+
116214
### **TypeScript**
117215

118216
```ts
@@ -154,12 +252,15 @@ function dfs(grid1: number[][], grid2: number[][], i: number, j: number): boolea
154252
```cpp
155253
class Solution {
156254
public:
157-
int countSubIslands(vector<vector<int>>& grid1, vector<vector<int>>& grid2) {
255+
int countSubIslands(vector<vector<int>> &grid1, vector<vector<int>> &grid2) {
158256
int m = grid1.size(), n = grid1[0].size();
159257
int count = 0;
160-
for (int i = 0; i < m; ++i) {
161-
for (int j = 0; j < n; ++j) {
162-
if (grid2[i][j] == 1 && dfs(grid1, grid2, i, j, m, n)) {
258+
for (int i = 0; i < m; ++i)
259+
{
260+
for (int j = 0; j < n; ++j)
261+
{
262+
if (grid2[i][j] == 1 && dfs(grid1, grid2, i, j, m, n))
263+
{
163264
++count;
164265
}
165266
}
@@ -168,15 +269,18 @@ public:
168269
}
169270

170271
private:
171-
vector<vector<int>> directions = {{0, 1}, {0, - 1}, {1, 0}, {-1, 0}};
172-
bool dfs(vector<vector<int>>& grid1, vector<vector<int>>& grid2, int i, int j, int m, int n) {
272+
vector<vector<int>> directions = {{0, 1}, {0, -1}, {1, 0}, {-1, 0}};
273+
bool dfs(vector<vector<int>> &grid1, vector<vector<int>> &grid2, int i, int j, int m, int n) {
173274
bool res = grid1[i][j] == 1;
174275
grid2[i][j] = 0;
175276

176-
for (auto direction : directions) {
277+
for (auto direction : directions)
278+
{
177279
int a = i + direction[0], b = j + direction[1];
178-
if (a >= 0 && a < m && b >= 0 && b < n && grid2[a][b] == 1) {
179-
if (!dfs(grid1, grid2, a, b, m, n)) {
280+
if (a >= 0 && a < m && b >= 0 && b < n && grid2[a][b] == 1)
281+
{
282+
if (!dfs(grid1, grid2, a, b, m, n))
283+
{
180284
res = false;
181285
}
182286
}

‎solution/1900-1999/1905.Count Sub Islands/README_EN.md

+114-10
Original file line numberDiff line numberDiff line change
@@ -43,12 +43,14 @@ The 1s colored red in grid2 are those considered to be part of a sub-island. The
4343

4444
## Solutions
4545

46-
DFS.
46+
DFS or Union find.
4747

4848
<!-- tabs:start -->
4949

5050
### **Python3**
5151

52+
DFS:
53+
5254
```python
5355
class Solution:
5456
def countSubIslands(self, grid1: List[List[int]], grid2: List[List[int]]) -> int:
@@ -71,8 +73,45 @@ class Solution:
7173
return count
7274
```
7375

76+
Union find:
77+
78+
```python
79+
class Solution:
80+
def countSubIslands(self, grid1: List[List[int]], grid2: List[List[int]]) -> int:
81+
m, n = len(grid1), len(grid1[0])
82+
p = list(range(m * n))
83+
84+
def find(x):
85+
if p[x] != x:
86+
p[x] = find(p[x])
87+
return p[x]
88+
89+
for i in range(m):
90+
for j in range(n):
91+
if grid2[i][j] == 1:
92+
idx = i * n + j
93+
if i < m - 1 and grid2[i + 1][j] == 1:
94+
p[find(idx)] = find((i + 1) * n + j)
95+
if j < n - 1 and grid2[i][j + 1] == 1:
96+
p[find(idx)] = find(i * n + j + 1)
97+
98+
s = [0] * (m * n)
99+
for i in range(m):
100+
for j in range(n):
101+
if grid2[i][j] == 1:
102+
s[find(i * n + j)] = 1
103+
for i in range(m):
104+
for j in range(n):
105+
root = find(i * n + j)
106+
if s[root] and grid1[i][j] == 0:
107+
s[root] = 0
108+
return sum(s)
109+
```
110+
74111
### **Java**
75112

113+
DFS:
114+
76115
```java
77116
class Solution {
78117
private int[][] directions = {{0, 1}, {0, - 1}, {1, 0}, {-1, 0}};
@@ -107,6 +146,65 @@ class Solution {
107146
}
108147
```
109148

149+
Union find:
150+
151+
```java
152+
class Solution {
153+
private int[] p;
154+
155+
public int countSubIslands(int[][] grid1, int[][] grid2) {
156+
int m = grid2.length, n = grid2[0].length;
157+
p = new int[m * n];
158+
for (int i = 0; i < p.length; ++i) {
159+
p[i] = i;
160+
}
161+
for (int i = 0; i < m; ++i) {
162+
for (int j = 0; j < n; ++j) {
163+
if (grid2[i][j] == 1) {
164+
int idx = i * n + j;
165+
if (i < m - 1 && grid2[i + 1][j] == 1) {
166+
p[find(idx)] = find((i + 1) * n + j);
167+
}
168+
if (j < n - 1 && grid2[i][j + 1] == 1) {
169+
p[find(idx)] = find(i * n + j + 1);
170+
}
171+
}
172+
}
173+
}
174+
boolean[] s = new boolean[m * n];
175+
for (int i = 0; i < m; ++i) {
176+
for (int j = 0; j < n; ++j) {
177+
if (grid2[i][j] == 1) {
178+
s[find(i * n + j)] = true;
179+
}
180+
}
181+
}
182+
for (int i = 0; i < m; ++i) {
183+
for (int j = 0; j < n; ++j) {
184+
int root = find(i * n + j);
185+
if (s[root] && grid1[i][j] == 0) {
186+
s[root] = false;
187+
}
188+
}
189+
}
190+
int res = 0;
191+
for (boolean e : s) {
192+
if (e) {
193+
++res;
194+
}
195+
}
196+
return res;
197+
}
198+
199+
private int find(int x) {
200+
if (p[x] != x) {
201+
p[x] = find(p[x]);
202+
}
203+
return p[x];
204+
}
205+
}
206+
```
207+
110208
### **TypeScript**
111209

112210
```ts
@@ -148,12 +246,15 @@ function dfs(grid1: number[][], grid2: number[][], i: number, j: number): boolea
148246
```cpp
149247
class Solution {
150248
public:
151-
int countSubIslands(vector<vector<int>>& grid1, vector<vector<int>>& grid2) {
249+
int countSubIslands(vector<vector<int>> &grid1, vector<vector<int>> &grid2) {
152250
int m = grid1.size(), n = grid1[0].size();
153251
int count = 0;
154-
for (int i = 0; i < m; ++i) {
155-
for (int j = 0; j < n; ++j) {
156-
if (grid2[i][j] == 1 && dfs(grid1, grid2, i, j, m, n)) {
252+
for (int i = 0; i < m; ++i)
253+
{
254+
for (int j = 0; j < n; ++j)
255+
{
256+
if (grid2[i][j] == 1 && dfs(grid1, grid2, i, j, m, n))
257+
{
157258
++count;
158259
}
159260
}
@@ -162,15 +263,18 @@ public:
162263
}
163264

164265
private:
165-
vector<vector<int>> directions = {{0, 1}, {0, - 1}, {1, 0}, {-1, 0}};
166-
bool dfs(vector<vector<int>>& grid1, vector<vector<int>>& grid2, int i, int j, int m, int n) {
266+
vector<vector<int>> directions = {{0, 1}, {0, -1}, {1, 0}, {-1, 0}};
267+
bool dfs(vector<vector<int>> &grid1, vector<vector<int>> &grid2, int i, int j, int m, int n) {
167268
bool res = grid1[i][j] == 1;
168269
grid2[i][j] = 0;
169270

170-
for (auto direction : directions) {
271+
for (auto direction : directions)
272+
{
171273
int a = i + direction[0], b = j + direction[1];
172-
if (a >= 0 && a < m && b >= 0 && b < n && grid2[a][b] == 1) {
173-
if (!dfs(grid1, grid2, a, b, m, n)) {
274+
if (a >= 0 && a < m && b >= 0 && b < n && grid2[a][b] == 1)
275+
{
276+
if (!dfs(grid1, grid2, a, b, m, n))
277+
{
174278
res = false;
175279
}
176280
}

‎solution/1900-1999/1905.Count Sub Islands/Solution.cpp

+15-9
Original file line numberDiff line numberDiff line change
@@ -1,11 +1,14 @@
11
class Solution {
22
public:
3-
int countSubIslands(vector<vector<int>>& grid1, vector<vector<int>>& grid2) {
3+
int countSubIslands(vector<vector<int>> &grid1, vector<vector<int>> &grid2) {
44
int m = grid1.size(), n = grid1[0].size();
55
int count = 0;
6-
for (int i = 0; i < m; ++i) {
7-
for (int j = 0; j < n; ++j) {
8-
if (grid2[i][j] == 1 && dfs(grid1, grid2, i, j, m, n)) {
6+
for (int i = 0; i < m; ++i)
7+
{
8+
for (int j = 0; j < n; ++j)
9+
{
10+
if (grid2[i][j] == 1 && dfs(grid1, grid2, i, j, m, n))
11+
{
912
++count;
1013
}
1114
}
@@ -14,15 +17,18 @@ class Solution {
1417
}
1518

1619
private:
17-
vector<vector<int>> directions = {{0, 1}, {0, - 1}, {1, 0}, {-1, 0}};
18-
bool dfs(vector<vector<int>>& grid1, vector<vector<int>>& grid2, int i, int j, int m, int n) {
20+
vector<vector<int>> directions = {{0, 1}, {0, -1}, {1, 0}, {-1, 0}};
21+
bool dfs(vector<vector<int>> &grid1, vector<vector<int>> &grid2, int i, int j, int m, int n) {
1922
bool res = grid1[i][j] == 1;
2023
grid2[i][j] = 0;
2124

22-
for (auto direction : directions) {
25+
for (auto direction : directions)
26+
{
2327
int a = i + direction[0], b = j + direction[1];
24-
if (a >= 0 && a < m && b >= 0 && b < n && grid2[a][b] == 1) {
25-
if (!dfs(grid1, grid2, a, b, m, n)) {
28+
if (a >= 0 && a < m && b >= 0 && b < n && grid2[a][b] == 1)
29+
{
30+
if (!dfs(grid1, grid2, a, b, m, n))
31+
{
2632
res = false;
2733
}
2834
}

‎solution/1900-1999/1905.Count Sub Islands/Solution.py

+1-1
Original file line numberDiff line numberDiff line change
@@ -9,7 +9,7 @@ def dfs(grid1, grid2, i, j, m, n) -> bool:
99
if not dfs(grid1, grid2, a, b, m, n):
1010
res = False
1111
return res
12-
12+
1313
m, n = len(grid1), len(grid1[0])
1414
count = 0
1515
for i in range(m):

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