結果

問題 No.1553 Lovely City
コンテスト
ユーザー neterukun
提出日時 2021-06-18 21:50:32
言語 PyPy3
(7.3.15)
結果
AC  
実行時間 1,462 ms / 2,000 ms
コード長 3,605 bytes
コンパイル時間 318 ms
コンパイル使用メモリ 82,304 KB
実行使用メモリ 241,428 KB
最終ジャッジ日時 2024-06-22 20:15:01
合計ジャッジ時間 29,242 ms
ジャッジサーバーID
（参考情報） 		judge1 / judge2
このコードへのチャレンジ
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ファイルパターン 結果
sample AC * 2
other AC * 26
権限があれば一括ダウンロードができます

ソースコード

diff # 

import sys
input = sys.stdin.buffer.readline


class UnionFind:
    def __init__(self, n):
        self.parent = [-1] * n
        self.n = n
        self.cnt = n

    def root(self, x):
        if self.parent[x] < 0:
            return x
        else:
            self.parent[x] = self.root(self.parent[x])
            return self.parent[x]

    def merge(self, x, y):
        x = self.root(x)
        y = self.root(y)
        if x == y:
            return False
        if self.parent[x] > self.parent[y]:
            x, y = y, x
        self.parent[x] += self.parent[y]
        self.parent[y] = x
        self.cnt -= 1
        return True

    def same(self, x, y):
        return self.root(x) == self.root(y)

    def size(self, x):
        return -self.parent[self.root(x)]

    def count(self):
        return self.cnt

    def groups(self):
        res = [[] for _ in range(self.n)]
        for i in range(self.n):
            res[self.root(i)].append(i)
        return [group for group in res if group]


class StronglyConnectedComponents:
    def __init__(self, n):
        self.n = n
        self.graph = [[] for _ in range(n)]
        self.rev_graph = [[] for _ in range(n)]
        self.labels = [-1] * n
        self.lb_cnt = 0

    def add_edge(self, v, nxt_v):
        self.graph[v].append(nxt_v)
        self.rev_graph[nxt_v].append(v)

    def build(self):
        self.post_order = []
        self.used = [False] * self.n
        for v in range(self.n):
            if not self.used[v]:
                self._dfs(v)

        for v in reversed(self.post_order):
            if self.labels[v] == -1:
                self._rev_dfs(v)
                self.lb_cnt += 1

    def _dfs(self, v):
        stack = [v, 0]
        while stack:
            v, idx = stack[-2:]
            if not idx and self.used[v]:
                stack.pop()
                stack.pop()
            else:
                self.used[v] = True
                if idx < len(self.graph[v]):
                    stack[-1] += 1
                    stack.append(self.graph[v][idx])
                    stack.append(0)
                else:
                    stack.pop()
                    self.post_order.append(stack.pop())

    def _rev_dfs(self, v):
        stack = [v]
        self.labels[v] = self.lb_cnt
        while stack:
            v = stack.pop()
            for nxt_v in self.rev_graph[v]:
                if self.labels[nxt_v] != -1:
                    continue
                stack.append(nxt_v)
                self.labels[nxt_v] = self.lb_cnt

    def construct_dag(self):
        self.dag = [[] for i in range(self.lb_cnt)]
        self.groups = [[] for i in range(self.lb_cnt)]
        for v, lb in enumerate(self.labels):
            for nxt_v in self.graph[v]:
                nxt_lb = self.labels[nxt_v]
                if lb == nxt_lb:
                    continue
                self.dag[lb].append(nxt_lb)
            self.groups[lb].append(v)
        return self.dag, self.groups


n, m = map(int, input().split())
edges = [list(map(int, input().split())) for i in range(m)]

    
scc = StronglyConnectedComponents(n)
uf = UnionFind(n)
for u, v in edges:
    u -= 1
    v -= 1
    scc.add_edge(u, v)
    uf.merge(u, v)

scc.build()
dag, group = scc.construct_dag()


ans = []
for gp in uf.groups():
    gp = sorted(gp, key=lambda x: scc.labels[x])
    lb = [scc.labels[i] for i in gp]
    for i in range(len(gp) - 1):
        ans.append((gp[i] + 1, gp[i + 1] + 1))
    if len(set(lb)) != len(lb):
        ans.append((gp[-1] + 1, gp[0] + 1))

print(len(ans))
for res in ans:
    print(*res)
0