feat: add solutions to lc problem: No.0200.Number of Islands

Author: yanglbme

solution/0200-0299/0200.Number of Islands/README.md

@@ -49,58 +49,275 @@
 	<li><code>grid[i][j]</code> 的值为 <code>'0'</code> 或 <code>'1'</code></li>
 </ul>
 
-
 ## 解法
 
 <!-- 这里可写通用的实现逻辑 -->
 
-BFS/DFS 均可
+BFS、DFS、并查集均可。
 
 <!-- tabs:start -->
 
 ### **Python3**
 
 <!-- 这里可写当前语言的特殊实现逻辑 -->
 
-```python
+并查集：
 
+```python
+class Solution:
+    def numIslands(self, grid: List[List[str]]) -> int:
+        m, n = len(grid), len(grid[0])
+        p = [-1] * (m * n)
+
+        def find(x):
+            if p[x] != x:
+                p[x] = find(p[x])
+            return p[x]
+
+        for i in range(m):
+            for j in range(n):
+                if grid[i][j] == '1':
+                    p[i * n + j] = i * n + j
+
+        for i in range(m):
+            for j in range(n):
+                if grid[i][j] == '1':
+                    if i < m - 1 and grid[i + 1][j] == '1':
+                        a, b = i * n + j, (i + 1) * n + j
+                        p[find(a)] = find(b)
+                    if j < n - 1 and grid[i][j + 1] == '1':
+                        a, b = i * n + j, i * n + j + 1
+                        p[find(a)] = find(b)
+        
+        cnt = 0
+        for i in range(m):
+            for j in range(n):
+                if i * n + j == find(i * n + j):
+                    cnt += 1
+        return cnt
 ```
 
 ### **Java**
 
 <!-- 这里可写当前语言的特殊实现逻辑 -->
 
+DFS：
+
 ```java
+class Solution {
+    public int numIslands(char[][] grid) {
+        int islandNum = 0;
+        for (int i = 0; i < grid.length; i++) {
+            for (int j = 0; j < grid[0].length; j++) {
+                if (grid[i][j] == '1') {
+                    infect(grid, i, j);
+                    islandNum ++;
+                }
+            }
+        }
+        return islandNum;
+    }
 
+    public void infect(char[][] grid, int i, int j) {
+        if (i < 0 || i >= grid.length ||
+                j < 0 || j >= grid[0].length ||
+                grid[i][j] != '1') {
+            return;
+        }
+        grid[i][j] = '2';
+        infect(grid, i + 1, j);
+        infect(grid, i - 1, j);
+        infect(grid, i, j + 1);
+        infect(grid, i, j - 1);
+    }
+}
+```
+
+并查集：
+
+```java
+class Solution {
+    private int[] p;
+
+    public int numIslands(char[][] grid) {
+        int m = grid.length, n = grid[0].length;
+        p = new int[m * n];
+        for (int i = 0; i < m; ++i) {
+            for (int j = 0; j < n; ++j) {
+                p[i * n + j] = grid[i][j] == '1' ? i * n + j : -1;
+            }
+        }
+        for (int i = 0; i < m; ++i) {
+            for (int j = 0; j < n; ++j) {
+                if (grid[i][j] == '1') {
+                    if (i < m - 1 && grid[i + 1][j] == '1') {
+                        p[find(i * n + j)] = find((i + 1) * n + j);
+                    }
+                    if (j < n - 1 && grid[i][j + 1] == '1') {
+                        p[find(i * n + j)] = find(i * n + j + 1);
+                    }
+                }
+            }
+        }
+        int cnt = 0;
+        for (int i = 0; i < m; ++i) {
+            for (int j = 0; j < n; ++j) {
+                if (p[i * n + j] != -1 && i * n + j == find(i * n + j)) {
+                    ++cnt;
+                }
+            }
+        }
+        return cnt;
+    }
+
+    private int find(int x) {
+        if (p[x] != x) {
+            p[x] = find(p[x]);
+        }
+        return p[x];
+    }
+}
 ```
 
 ### **TypeScript**
 
 ```ts
 function numIslands(grid: string[][]): number {
-    let m = grid.length, n = grid[0].length;
-    let ans = 0;
-    for (let i = 0; i < m; ++i) {
-        for (let j = 0; j < n; ++j) {
-            if (grid[i][j] == '1') {
-                dfs(grid, i, j);
-                ++ans;
-            }
-        }
+  let m = grid.length,
+    n = grid[0].length;
+  let ans = 0;
+  for (let i = 0; i < m; ++i) {
+    for (let j = 0; j < n; ++j) {
+      if (grid[i][j] == "1") {
+        dfs(grid, i, j);
+        ++ans;
+      }
     }
-    return ans;
-};
+  }
+  return ans;
+}
 
 function dfs(grid: string[][], i: number, j: number) {
-    let m = grid.length, n = grid[0].length;
-    if (i < 0 || i > m - 1 || j < 0 || j > n - 1 || grid[i][j] == '0') {
-        return;
+  let m = grid.length,
+    n = grid[0].length;
+  if (i < 0 || i > m - 1 || j < 0 || j > n - 1 || grid[i][j] == "0") {
+    return;
+  }
+  grid[i][j] = "0";
+  for (let [dx, dy] of [
+    [0, 1],
+    [0, -1],
+    [1, 0],
+    [-1, 0],
+  ]) {
+    let x = i + dx,
+      y = j + dy;
+    dfs(grid, x, y);
+  }
+}
+```
+
+### **C++**
+
+```cpp
+class Solution {
+public:
+    vector<int> p;
+
+    int numIslands(vector<vector<char>> &grid) {
+        int m = grid.size(), n = grid[0].size();
+        p.resize(m * n);
+        for (int i = 0; i < m; ++i)
+        {
+            for (int j = 0; j < n; ++j)
+            {
+                p[i * n + j] = grid[i][j] == '1' ? i * n + j : -1;
+            }
+        }
+        for (int i = 0; i < m; ++i)
+        {
+            for (int j = 0; j < n; ++j)
+            {
+                if (grid[i][j] == '1')
+                {
+                    if (i < m - 1 && grid[i + 1][j] == '1')
+                    {
+                        p[find(i * n + j)] = find((i + 1) * n + j);
+                    }
+                    if (j < n - 1 && grid[i][j + 1] == '1')
+                    {
+                        p[find(i * n + j)] = find(i * n + j + 1);
+                    }
+                }
+            }
+        }
+        int cnt = 0;
+        for (int i = 0; i < m; ++i)
+        {
+            for (int j = 0; j < n; ++j)
+            {
+                if (p[i * n + j] != -1 && i * n + j == find(i * n + j))
+                    ++cnt;
+            }
+        }
+        return cnt;
     }
-    grid[i][j] = '0';
-    for (let [dx, dy] of [[0, 1], [0, -1], [1, 0], [-1, 0]]) {
-        let x = i + dx, y = j + dy;
-        dfs(grid, x, y);
+
+    int find(int x) {
+        if (p[x] != x)
+        {
+            p[x] = find(p[x]);
+        }
+        return p[x];
     }
+};
+```
+
+### **Go**
+
+```go
+var p []int
+
+func numIslands(grid [][]byte) int {
+	m, n := len(grid), len(grid[0])
+	p = make([]int, m*n)
+	for i := 0; i < m; i++ {
+		for j := 0; j < n; j++ {
+			if grid[i][j] == '1' {
+				p[i*n+j] = i*n + j
+			} else {
+				p[i*n+j] = -1
+			}
+		}
+	}
+	for i := 0; i < m; i++ {
+		for j := 0; j < n; j++ {
+			if grid[i][j] == '1' {
+				if i < m-1 && grid[i+1][j] == '1' {
+					p[find(i*n+j)] = find((i+1)*n + j)
+				}
+				if j < n-1 && grid[i][j+1] == '1' {
+					p[find(i*n+j)] = find(i*n + j + 1)
+				}
+			}
+		}
+	}
+	cnt := 0
+	for i := 0; i < m; i++ {
+		for j := 0; j < n; j++ {
+			if p[i*n+j] != -1 && i*n+j == find(i*n+j) {
+				cnt++
+			}
+		}
+	}
+	return cnt
+}
+
+func find(x int) int {
+	if p[x] != x {
+		p[x] = find(p[x])
+	}
+	return p[x]
 }
 ```