## 851. Loud and Rich

In a group of N people (labelled `0, 1, 2, ..., N-1`

), each person has different amounts of money, and different levels of quietness.

For convenience, we'll call the person with label `x`

, simply "person `x`

".

We'll say that `richer[i] = [x, y]`

if person `x`

definitely has more money than person `y`

. Note that `richer`

may only be a subset of valid observations.

Also, we'll say `quiet[x] = q`

if person x has quietness `q`

.

Now, return `answer`

, where `answer[x] = y`

if `y`

is the least quiet person (that is, the person `y`

with the smallest value of `quiet[y]`

), among all people who definitely have equal to or more money than person `x`

.

**Example 1:**

Input:richer = [[1,0],[2,1],[3,1],[3,7],[4,3],[5,3],[6,3]], quiet = [3,2,5,4,6,1,7,0]Output:[5,5,2,5,4,5,6,7]Explanation:answer[0] = 5. Person 5 has more money than 3, which has more money than 1, which has more money than 0. The only person who is quieter (has lower quiet[x]) is person 7, but it isn't clear if they have more money than person 0. answer[7] = 7. Among all people that definitely have equal to or more money than person 7 (which could be persons 3, 4, 5, 6, or 7), the person who is the quietest (has lower quiet[x]) is person 7. The other answers can be filled out with similar reasoning.

**Note:**

`1 <= quiet.length = N <= 500`

`0 <= quiet[i] < N`

, all`quiet[i]`

are different.`0 <= richer.length <= N * (N-1) / 2`

`0 <= richer[i][j] < N`

`richer[i][0] != richer[i][1]`

`richer[i]`

's are all different.- The observations in
`richer`

are all logically consistent.

## Rust Solution

```
struct Solution;
use std::collections::HashSet;
impl Solution {
fn loud_and_rich(richer: Vec<Vec<i32>>, quiet: Vec<i32>) -> Vec<i32> {
let n = quiet.len();
let mut graph: Vec<HashSet<usize>> = vec![HashSet::new(); n];
for e in richer {
let u = e[0] as usize;
let v = e[1] as usize;
graph[v].insert(u);
}
let mut res = vec![n; n];
for i in 0..n {
Self::dfs(i, &mut res, &graph, &quiet, n);
}
res.into_iter().map(|x| x as i32).collect()
}
fn dfs(
u: usize,
stack: &mut Vec<usize>,
graph: &[HashSet<usize>],
quiet: &[i32],
n: usize,
) -> usize {
if stack[u] == n {
stack[u] = u;
for &v in &graph[u] {
let w = Self::dfs(v, stack, graph, quiet, n);
if quiet[w] < quiet[stack[u]] {
stack[u] = w;
}
}
}
stack[u]
}
}
#[test]
fn test() {
let richer = vec_vec_i32![[1, 0], [2, 1], [3, 1], [3, 7], [4, 3], [5, 3], [6, 3]];
let quiet = vec![3, 2, 5, 4, 6, 1, 7, 0];
let res = vec![5, 5, 2, 5, 4, 5, 6, 7];
assert_eq!(Solution::loud_and_rich(richer, quiet), res);
}
```

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