#725826 (PyPy3) No.1813 Magical Stones

• 問題: No.1813 Magical Stones
• ユーザー: MasKoaTS
• 提出日時: 2021-12-22 14:01:09
• 言語: PyPy3 (7.3.15)
• 結果: AC
• 実行時間: 478 ms / 2,000 ms
• コード長: 2,280 bytes
• コンパイル時間: 174 ms
• コンパイル使用メモリ: 82,176 KB
• 実行使用メモリ: 111,712 KB
• 最終ジャッジ日時: 2024-09-16 08:36:30
• 合計ジャッジ時間: 11,485 ms
• ジャッジサーバーID （参考情報）: judge4 / judge6

ファイルパターン	結果
sample	AC * 4
other	AC * 40

ソースコード

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import sys
input = sys.stdin.readline
"""
強連結成分分解（SCC）
from : https://github.com/ryusuke920/kyopro_educational_90_python/blob/main/solve_python/021.py
ref : https://manabitimes.jp/math/1250
"""
class SCC:
    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
    
    #グラフに有向辺を追加（逆向きのものを含む）
    def add_edge(self, v, nxt_v):
        self.graph[v].append(nxt_v)
        self.rev_graph[nxt_v].append(v)
    #SCCグラフの構成
    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
    #SCCグラフを作る上でのDFS
    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())
    #逆向きDFS
    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
    #構成し終えたSCCグラフを連結成分ごとにリストにする
    def construct(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
"""
Main Code
"""
n,m = map(int, input().split())
scc = SCC(n)
for _ in [0] * m:
    a,b = map(int, input().split())
    a -= 1; b -= 1
    scc.add_edge(a,b)
scc.build()
dag,_ = scc.construct()
t = len(dag)
if(t == 1):
    print(0)
    exit(0)
source = [True] * t
sink = [True] * t
for i in range(t):
    for j in dag[i]:
        sink[i] = source[j] = False
ans = max(sum(source),sum(sink))
print(ans)
 
 
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