solutions/2924-find-champion-ii.js

/**
 * 2924. Find Champion II
 * https://leetcode.com/problems/find-champion-ii/
 * Difficulty: Medium
 *
 * 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.
 */

/**
 * @param {number} n
 * @param {number[][]} edges
 * @return {number}
 */
var findChampion = function(n, edges) {
  const inDegree = new Array(n).fill(0);

  for (const [, v] of edges) {
    inDegree[v]++;
  }
  let champion = -1;
  for (let i = 0; i < n; i++) {
    if (inDegree[i] === 0) {
      if (champion !== -1) return -1;
      champion = i;
    }
  }

  return champion;
};