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Sep 15, 2023
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feat: add solutions to lc problem: No.2192 #1631

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203 changes: 113 additions & 90 deletions ...on/2100-2199/2192.All Ancestors of a Node in a Directed Acyclic Graph/README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -67,6 +67,12 @@

**方法一：BFS**

我们先根据二维数组 $edges$ 构建邻接表 $g$，其中 $g[i]$ 表示节点 $i$ 的所有后继节点。

然后我们从小到大枚举节点 $i$ 作为祖先节点，使用 BFS 搜索节点 $i$ 的所有后继节点，把节点 $i$ 加入这些后继节点的祖先列表中。

时间复杂度 $O(n^2)$，空间复杂度 $O(n^2)$。其中 $n$ 是节点数。

<!-- tabs:start -->

### **Python3**
Expand All @@ -76,27 +82,23 @@
```python
class Solution:
def getAncestors(self, n: int, edges: List[List[int]]) -> List[List[int]]:
def bfs(s: int):
q = deque([s])
vis = {s}
while q:
i = q.popleft()
for j in g[i]:
if j not in vis:
vis.add(j)
q.append(j)
ans[j].append(s)

g = defaultdict(list)
for u, v in edges:
g[v].append(u)
ans = []
g[u].append(v)
ans = [[] for _ in range(n)]
for i in range(n):
if not g[i]:
ans.append([])
continue
q = deque([i])
vis = [False] * n
vis[i] = True
t = []
while q:
for _ in range(len(q)):
v = q.popleft()
for u in g[v]:
if not vis[u]:
vis[u] = True
q.append(u)
t.append(u)
ans.append(sorted(t))
bfs(i)
return ans
```

Expand All @@ -106,39 +108,42 @@ class Solution:

```java
class Solution {
private int n;
private List<Integer>[] g;
private List<List<Integer>> ans;

public List<List<Integer>> getAncestors(int n, int[][] edges) {
List<Integer>[] g = new List[n];
Arrays.setAll(g, k -> new ArrayList<>());
for (int[] e : edges) {
g[e[1]].add(e[0]);
g = new List[n];
this.n = n;
Arrays.setAll(g, i -> new ArrayList<>());
for (var e : edges) {
g[e[0]].add(e[1]);
}
List<List<Integer>> ans = new ArrayList<>();
ans = new ArrayList<>();
for (int i = 0; i < n; ++i) {
List<Integer> t = new ArrayList<>();
if (g[i].isEmpty()) {
ans.add(t);
continue;
}
Deque<Integer> q = new ArrayDeque<>();
q.offer(i);
boolean[] vis = new boolean[n];
vis[i] = true;
while (!q.isEmpty()) {
for (int j = q.size(); j > 0; --j) {
int v = q.poll();
for (int u : g[v]) {
if (!vis[u]) {
vis[u] = true;
q.offer(u);
t.add(u);
}
}
ans.add(new ArrayList<>());
}
for (int i = 0; i < n; ++i) {
bfs(i);
}
return ans;
}

private void bfs(int s) {
Deque<Integer> q = new ArrayDeque<>();
q.offer(s);
boolean[] vis = new boolean[n];
vis[s] = true;
while (!q.isEmpty()) {
int i = q.poll();
for (int j : g[i]) {
if (!vis[j]) {
vis[j] = true;
q.offer(j);
ans.get(j).add(s);
}
}
Collections.sort(t);
ans.add(t);
}
return ans;
}
}
```
Expand All @@ -149,32 +154,31 @@ class Solution {
class Solution {
public:
vector<vector<int>> getAncestors(int n, vector<vector<int>>& edges) {
vector<vector<int>> g(n);
for (auto& e : edges) g[e[1]].push_back(e[0]);
vector<vector<int>> ans;
for (int i = 0; i < n; ++i) {
vector<int> t;
if (g[i].empty()) {
ans.push_back(t);
continue;
}
queue<int> q{{i}};
vector<bool> vis(n);
vis[i] = true;
while (!q.empty()) {
for (int j = q.size(); j > 0; --j) {
int v = q.front();
q.pop();
for (int u : g[v]) {
if (vis[u]) continue;
vis[u] = true;
q.push(u);
t.push_back(u);
vector<int> g[n];
for (auto& e : edges) {
g[e[0]].push_back(e[1]);
}
vector<vector<int>> ans(n);
auto bfs = [&](int s) {
queue<int> q;
q.push(s);
bool vis[n];
memset(vis, 0, sizeof(vis));
vis[s] = true;
while (q.size()) {
int i = q.front();
q.pop();
for (int j : g[i]) {
if (!vis[j]) {
vis[j] = true;
ans[j].push_back(s);
q.push(j);
}
}
}
sort(t.begin(), t.end());
ans.push_back(t);
};
for (int i = 0; i < n; ++i) {
bfs(i);
}
return ans;
}
Expand All @@ -187,33 +191,27 @@ public:
func getAncestors(n int, edges [][]int) [][]int {
g := make([][]int, n)
for _, e := range edges {
g[e[1]] = append(g[e[1]], e[0])
g[e[0]] = append(g[e[0]], e[1])
}
var ans [][]int
for i := 0; i < n; i++ {
var t []int
if len(g[i]) == 0 {
ans = append(ans, t)
continue
}
q := []int{i}
ans := make([][]int, n)
bfs := func(s int) {
q := []int{s}
vis := make([]bool, n)
vis[i] = true
vis[s] = true
for len(q) > 0 {
for j := len(q); j > 0; j-- {
v := q[0]
q = q[1:]
for _, u := range g[v] {
if !vis[u] {
vis[u] = true
q = append(q, u)
t = append(t, u)
}
i := q[0]
q = q[1:]
for _, j := range g[i] {
if !vis[j] {
vis[j] = true
q = append(q, j)
ans[j] = append(ans[j], s)
}
}
}
sort.Ints(t)
ans = append(ans, t)
}
for i := 0; i < n; i++ {
bfs(i)
}
return ans
}
Expand All @@ -222,7 +220,32 @@ func getAncestors(n int, edges [][]int) [][]int {
### **TypeScript**

```ts

function getAncestors(n: number, edges: number[][]): number[][] {
const g: number[][] = Array.from({ length: n }, () => []);
for (const [u, v] of edges) {
g[u].push(v);
}
const ans: number[][] = Array.from({ length: n }, () => []);
const bfs = (s: number) => {
const q: number[] = [s];
const vis: boolean[] = Array.from({ length: n }, () => false);
vis[s] = true;
while (q.length) {
const i = q.shift()!;
for (const j of g[i]) {
if (!vis[j]) {
vis[j] = true;
ans[j].push(s);
q.push(j);
}
}
}
};
for (let i = 0; i < n; ++i) {
bfs(i);
}
return ans;
}
```

### **...**
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