提出 #69496515

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ソースコード 拡げる

/* Code By WCM */
/*
Date:
大致思路：
复杂度：
期望得分：
*/
#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <ctime>
#include <iomanip>
#include <vector>
#include <queue>
#define pb push_back

using namespace std;

inline int read();
void write(int);
void writeln(int);

const int N = 2e5 + 5;
int n, a[N], b[N], ans;
vector <int> G[N];

void dfs(int u) {
	for(auto v : G[u]) {
		if(a[v]) continue;
		a[v] = 1, dfs(v);
	}
}

int main() {

//	freopen(".in", "r", stdin);
//	freopen(".out", "w", stdout);

	n = read();
	for(int i = 1; i <= n; i++) {
		int u = read(), v = read();
		G[u].pb(i), G[v].pb(i);
		if(u == 0 && v == 0) b[i] = a[i] = 1;
	}
	
	for(int i = 1; i <= n; i++) if(b[i]) dfs(i);
	for(int i = 1; i <= n; i++) ans += (a[i]);
	printf("%d\n", ans);
	
//	printf("\nThe time used: ");
//	printf("%.2lfs",(double)clock()/CLOCKS_PER_SEC);

	return 0;

}

inline int read() {
	int res = 0, f = 1;
	char ch = getchar();
	while( !(ch >= '0' && ch <= '9') ) {
		if(ch == '-') f = -1;
		ch = getchar();
	}
	while(ch >= '0' && ch <= '9') {
		res = (res << 1) + (res << 3) + (ch ^ 48);
		ch = getchar();
	}
	return res * f;
}

void write(int x) {
	static int sta[35];
	int top = 0;
	do {
		sta[top++] = x % 10;
		x /= 10;
	} while(x);
	while(top) putchar(sta[--top] ^ 48);
}

void writeln(int x) {
	write(x);
	putchar('\n');
}

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