P2661 信息传递(并查集，python）

1. 题目

原题

2. 题解

并查集找最小环。
使用 path_count 来计算节点和父亲节点的距离。

#!/usr/bin/env python
# encoding=utf-8
def init_parents(N):
    parents = {}
    path_count = {}
    for i in range(N):
        parents[i+1] = i+1
        path_count[i+1] = 0
    return parents, path_count

def find_parent(parents, path_count, x):
    if x != parents[x]:
        tmp = parents[x]
        parents[x] = find_parent(parents, path_count,parents[x])
        path_count[x] += path_count[tmp]
    return parents[x]

def union(parents, path_count,  x, y):
    root_x = find_parent(parents, path_count,x)
    root_y = find_parent(parents, path_count,y)
    if root_x == root_y:
        return True
    else:
        parents[root_x] = root_y
        path_count[x] = path_count[y]+1
    return False

def min_time_count(N, edge):
    # 1. 初始化
    parents, path_count = init_parents(N)
    graph = list(zip([i+1 for i in range(N)], edge))
    #print(graph)
    # 2. 合并:
    min_count = float("inf")

    for edge in graph:
        x, y = edge[0],edge[1]

        if not union(parents, path_count, x, y):
            #print(graph, parents, path_count)
            continue
        else:
        	# 节点和父亲节点的距离，在加上父亲节点。
            tmp = abs(path_count[x] - path_count[y]) + 1
            min_count = min(min_count,tmp)
            #print(graph, parents, path_count)

    return min_count

if __name__ == "__main__":
    # n = 5
    # T = [2,4,2,3,1]

    n = int(input())
    T = list(map(int, input().strip().split()))
    res = min_time_count(n,T)
    print(res)