Submission #102569

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Source Code Expand

#include <cstdio>
#include <vector>
#include <queue>
#include <iostream>

using namespace std;

struct edge {
	int src, dst;
	edge(int s, int d) : src(s), dst(d) { }
};
typedef vector<edge> edges;
typedef vector<edges> graph;

int D[100050], E[100050];
int Dc[100050], Ec[100050];

int main()
{
	int N, M, s, t;

	scanf("%d%d%d%d", &N, &M, &s, &t);
	--s; --t;

	graph G(N);
	for (int i = 0; i < M; ++i) {
		int x, y;
		scanf("%d%d", &x, &y);
		--x; --y;
		G[x].push_back(edge(x, y));
		G[y].push_back(edge(y, x));
	}

	for (int i = 0; i < N; ++i) D[i] = E[i] = 1001001001;

	queue<int> Q;
	Q.push(s); D[s] = 0;
	while (!Q.empty()) {
		int u = Q.front(); Q.pop();
		for (int i = 0; i < G[u].size(); ++i) {
			int v = G[u][i].dst;
			if (D[v] > D[u] + 1) {
				D[v] = D[u] + 1;
				Q.push(v);
			}
		}
	}

	Q = queue<int>();
	Q.push(t); E[t] = 0;
	while (!Q.empty()) {
		int u = Q.front(); Q.pop();
		for (int i = 0; i < G[u].size(); ++i) {
			int v = G[u][i].dst;
			if (E[v] > E[u] + 1) {
				E[v] = E[u] + 1;
				Q.push(v);
			}
		}
	}

	long long res = 0;
	for (int i = 0; i < N; ++i) {
		if (D[i] <= N) Dc[D[i]]++;
		if (E[i] <= N) Ec[E[i]]++;
	}

	for (int d = 0; d <= N; ++d) {
		int e = D[t] - d - 2;
		if (e >= 0 && e <= N && Dc[d] && Ec[e]) {
			// cerr << d << ' ' << e << ' ' << Dc[d] << ' ' << Ec[e] << endl;
			res += (long long)Dc[d] * Ec[e];
		}
	}

	printf("%lld\n", res);
	
	return 0;
}

Submission Info

Compile Error

./Main.cpp: In function ‘int main()’:
./Main.cpp:22: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result
./Main.cpp:28: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result

Judge Result