2924. Find Champion II

There are n teams numbered from 0 to n - 1 in a tournament; each team is also a node in a DAG.

You are given the integer n and a 0-indexed 2D integer array edges of length m representing the DAG, where edges[i] = [ui, vi] indicates that there is a directed edge from team ui to team vi in the graph.

A directed edge from a to b in the graph means that team a is stronger than team b and team b is weaker than team a.

Team a will be the champion of the tournament if there is no team b that is stronger than team a.

Return the team that will be the champion of the tournament if there is a unique champion, otherwise, return -1.

Notes

• A cycle is a series of nodes a1, a2, ..., an, an+1 such that node a1 is the same node as node an+1, the nodes a1, a2, ..., an are distinct, and there is a directed edge from the node ai to node ai+1 for every i in the range [1, n].
• A DAG is a directed graph that does not have any cycle.

class Solution {
public:
    int findChampion(int n, vector<vector<int>>& edges) {
        vector<int> ind(n);
        for(auto e : edges) {
            int u = e[0], v = e[1];
            ind[v] += 1;
        }
        int root = -1;
        for(int i = 0; i < n; i++) {
            if(ind[i]) continue;
            if(root == -1) root = i;
            else return -1;
        }
        return root;
    }
};