43 lines
981 B
C++
43 lines
981 B
C++
#include <iostream>
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#include <vector>
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using namespace std;
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const int NEG_INF = -1e9;
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int main() {
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int v, e;
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cin >> v >> e;
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vector<vector<int>> dp(v, vector<int>(v, NEG_INF));
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for (int i = 0; i < v; i++) dp[i][i] = 0; // 自环=0
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for (int i = 0; i < e; i++) {
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int a, b, w;
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cin >> a >> b >> w;
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dp[a - 1][b - 1] = max(dp[a - 1][b - 1], w); // 可能多条边，取最大
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}
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for (int k = 0; k < v; k++) {
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for (int i = 0; i < v; i++) {
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if (dp[i][k] <= NEG_INF / 2) continue;
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for (int j = 0; j < v; j++) {
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if (dp[k][j] <= NEG_INF / 2) continue;
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dp[i][j] = max(dp[i][j], dp[i][k] + dp[k][j]);
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}
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}
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}
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int mx = -1;
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for (int i = 0; i < v; i++) {
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for (int j = 0; j < v; j++) {
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if (dp[i][j] > NEG_INF / 2) {
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mx = max(mx, dp[i][j]);
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}
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}
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}
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mx == -1 ? cout << mx << endl;
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return 0;
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}
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