997. Find the Town Judge
use std::collections::{HashMap, HashSet}; /** 997. Find the Town Judge https://leetcode.com/problems/find-the-town-judge/ In a town, there are n people labeled from 1 to n. There is a rumor that one of these people is secretly the town judge. If the town judge exists, then: 1. The town judge trusts nobody. 2. Everybody (except for the town judge) trusts the town judge. 3. There is exactly one person that satisfies properties 1 and 2. You are given an array trust where trust[i] = [ai, bi] representing that the person labeled ai trusts the person labeled bi. Return the label of the town judge if the town judge exists and can be identified, or return -1 otherwise. Example 1: Input: n = 2, trust = [[1,2]] Output: 2 Example 2: Input: n = 3, trust = [[1,3],[2,3]] Output: 3 Example 3: Input: n = 3, trust = [[1,3],[2,3],[3,1]] Output: -1 Constraints: 1. 1 <= n <= 1000 2. 0 <= trust.length <= 10^4 3. trust[i].length == 2 4. All the pairs of trust are unique. 5. ai != bi 6. 1 <= ai, bi <= n */ pub struct Solution {} impl Solution { /* Solution: HashMap+HashSet, Time:O(n), Space:O(n) */ pub fn find_judge(n: i32, trust: Vec<Vec<i32>>) -> i32 { let count = trust.len(); if (count == 0) { //check some corner case return if n == 1 { 1 } else { -1 }; } let mut peoplesWillTrustAnother: HashSet<i32> = HashSet::new(); let mut mappingForJudge: HashMap<i32, Vec<i32>> = HashMap::new(); for i in 0..count { //[0] is can be trust other, there are should not be a Judge peoplesWillTrustAnother.insert(trust[i][0]); //key is someone and value is list of everyone who trusts that people let vec = mappingForJudge.entry(trust[i][1] as i32).or_insert(Vec::new()); vec.push(trust[i][0]); } /* Checking for Judge: 1. not in peoplesWillTrustAnother; 2. has N-1 peoples trusts */ for i in 1..n + 1 { if (peoplesWillTrustAnother.contains(&i)) { continue; } //if mappingForJudge.get(&i) can decomposed to array if let Some(array) = mappingForJudge.get(&i) { if (array.len() == (n - 1) as usize) { return i; } } } -1 } }