# Leetcode 1557. Minimum number of vertices to reach all nodes

## 計算所有節點入度

入度為零的節點加入答案中

class Solution:
    def findSmallestSetOfVertices(self, n: int, edges: List[List[int]]) -> List[int]:
        in_degree = [0] * n
        output = []
        for ai,bi in edges:
            in_degree[bi] += 1
        
        for i in range(n):
            degree = in_degree[i]
            if degree == 0:
                output.append(i)
        return output