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Commit 6a04399

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feat: add solutions to lc problem: No.1970.Last Day Where You Can Still Cross
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‎solution/1900-1999/1970.Last Day Where You Can Still Cross/README.md‎

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<li><code>cells</code>&nbsp;中的所有格子坐标都是 <strong>唯一</strong>&nbsp;的。</li>
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</ul>
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## 解法
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<!-- 这里可写通用的实现逻辑 -->
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逆序并查集。
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并查集模板:
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模板 1——朴素并查集:
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```python
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# 初始化,p存储每个点的父节点
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p = list(range(n))
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# 返回x的祖宗节点
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def find(x):
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if p[x] != x:
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# 路径压缩
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p[x] = find(p[x])
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return p[x]
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# 合并a和b所在的两个集合
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p[find(a)] = find(b)
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```
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模板 2——维护 size 的并查集:
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```python
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# 初始化,p存储每个点的父节点,size只有当节点是祖宗节点时才有意义,表示祖宗节点所在集合中,点的数量
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p = list(range(n))
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size = [1] * n
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# 返回x的祖宗节点
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def find(x):
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if p[x] != x:
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# 路径压缩
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p[x] = find(p[x])
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return p[x]
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# 合并a和b所在的两个集合
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if find(a) != find(b):
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size[find(b)] += size[find(a)]
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p[find(a)] = find(b)
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```
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模板 3——维护到祖宗节点距离的并查集:
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```python
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# 初始化,p存储每个点的父节点,d[x]存储x到p[x]的距离
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p = list(range(n))
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d = [0] * n
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# 返回x的祖宗节点
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def find(x):
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if p[x] != x:
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t = find(p[x])
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d[x] += d[p[x]]
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p[x] = t
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return p[x]
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# 合并a和b所在的两个集合
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p[find(a)] = find(b)
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d[find(a)] = distance
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```
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<!-- tabs:start -->
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### **Python3**
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<!-- 这里可写当前语言的特殊实现逻辑 -->
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```python
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class Solution:
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def latestDayToCross(self, row: int, col: int, cells: List[List[int]]) -> int:
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n = row * col
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p = list(range(n + 2))
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grid = [[False] * col for _ in range(row)]
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top, bottom = n, n + 1
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def find(x):
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if p[x] != x:
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p[x] = find(p[x])
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return p[x]
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def check(i, j):
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return 0 <= i < row and 0 <= j < col and grid[i][j]
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for k in range(len(cells) - 1, -1, -1):
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i, j = cells[k][0] - 1, cells[k][1] - 1
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grid[i][j] = True
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for x, y in [[0, 1], [0, -1], [1, 0], [-1, 0]]:
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if check(i + x, j + y):
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p[find(i * col + j)] = find((i + x) * col + j + y)
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if i == 0:
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p[find(i * col + j)] = find(top)
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if i == row - 1:
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p[find(i * col + j)] = find(bottom)
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if find(top) == find(bottom):
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return k
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return 0
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```
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### **Java**
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<!-- 这里可写当前语言的特殊实现逻辑 -->
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```java
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class Solution {
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private int[] p;
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private int row;
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private int col;
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private boolean[][] grid;
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private int[][] dirs = new int[][]{{0, -1}, {0, 1}, {1, 0}, {-1, 0}};
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public int latestDayToCross(int row, int col, int[][] cells) {
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int n = row * col;
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this.row = row;
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this.col = col;
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p = new int[n + 2];
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for (int i = 0; i < p.length; ++i) {
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p[i] = i;
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}
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grid = new boolean[row][col];
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int top = n, bottom = n + 1;
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for (int k = cells.length - 1; k >= 0; --k) {
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int i = cells[k][0] - 1, j = cells[k][1] - 1;
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grid[i][j] = true;
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for (int[] e : dirs) {
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if (check(i + e[0], j + e[1])) {
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p[find(i * col + j)] = find((i + e[0]) * col + j + e[1]);
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}
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}
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if (i == 0) {
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p[find(i * col + j)] = find(top);
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}
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if (i == row - 1) {
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p[find(i * col + j)] = find(bottom);
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}
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if (find(top) == find(bottom)) {
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return k;
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}
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}
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return 0;
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}
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private int find(int x) {
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if (p[x] != x) {
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p[x] = find(p[x]);
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}
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return p[x];
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}
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private boolean check(int i, int j) {
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return i >= 0 && i < row && j >= 0 && j < col && grid[i][j];
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}
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}
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```
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### **C++**
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```cpp
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class Solution {
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public:
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vector<int> p;
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int dirs[4][2] = {{0, -1}, {0, 1}, {1, 0}, {-1, 0}};
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int row, col;
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int latestDayToCross(int row, int col, vector<vector<int>>& cells) {
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int n = row * col;
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this->row = row;
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this->col = col;
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p.resize(n + 2);
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for (int i = 0; i < p.size(); ++i) p[i] = i;
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vector<vector<bool>> grid(row, vector<bool>(col, false));
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int top = n, bottom = n + 1;
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for (int k = cells.size() - 1; k >= 0; --k)
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{
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int i = cells[k][0] - 1, j = cells[k][1] - 1;
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grid[i][j] = true;
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for (auto e : dirs)
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{
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if (check(i + e[0], j + e[1], grid))
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{
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p[find(i * col + j)] = find((i + e[0]) * col + j + e[1]);
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}
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}
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if (i == 0) p[find(i * col + j)] = find(top);
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if (i == row - 1) p[find(i * col + j)] = find(bottom);
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if (find(top) == find(bottom)) return k;
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}
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return 0;
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}
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bool check(int i, int j, vector<vector<bool>>& grid) {
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return i >= 0 && i < row && j >= 0 && j < col && grid[i][j];
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}
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int find(int x) {
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if (p[x] != x) p[x] = find(p[x]);
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return p[x];
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}
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};
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```
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### **Go**
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```go
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var p []int
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func latestDayToCross(row int, col int, cells [][]int) int {
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n := row * col
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p = make([]int, n+2)
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for i := 0; i < len(p); i++ {
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p[i] = i
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}
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grid := make([][]bool, row)
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for i := 0; i < row; i++ {
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grid[i] = make([]bool, col)
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}
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top, bottom := n, n+1
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dirs := [4][2]int{{0, -1}, {0, 1}, {1, 0}, {-1, 0}}
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for k := len(cells) - 1; k >= 0; k-- {
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i, j := cells[k][0]-1, cells[k][1]-1
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grid[i][j] = true
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for _, e := range dirs {
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if check(i+e[0], j+e[1], grid) {
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p[find(i*col+j)] = find((i+e[0])*col + j + e[1])
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}
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}
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if i == 0 {
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p[find(i*col+j)] = find(top)
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}
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if i == row-1 {
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p[find(i*col+j)] = find(bottom)
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}
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if find(top) == find(bottom) {
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return k
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}
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}
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return 0
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}
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func check(i, j int, grid [][]bool) bool {
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return i >= 0 && i < len(grid) && j >= 0 && j < len(grid[0]) && grid[i][j]
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}
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func find(x int) int {
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if p[x] != x {
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p[x] = find(p[x])
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}
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return p[x]
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}
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```
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### **...**

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