Codeforces Round #374 (Div. 2) C. Journey DP

C. Journey

链接：

http://codeforces.com/contest/721/problem/C

题意：

给你一个n点m边的图，让你从1走到n，找到一条经过尽量多点的路径，且路径边权和小于等于T

然后输出路径。

题解：

直接DP，DP[i][j]表示在i点，当前经过了j个点的最小代价是多少

代码：

#include <iostream>  
#include <stack>   
#include <cstring>  
using namespace std;

const int maxn = 5e3 + 7;
struct Edge { int u, v, t; }E[maxn];
int dp[maxn][maxn];
int pre[maxn][maxn];
stack<int> ans;

int main()
{
    int n, m, T;
    cin >> n >> m >> T;
    for (int i = 0; i < m; i++)
        cin >> E[i].u >> E[i].v >> E[i].t;
    memset(dp, 0x3f, sizeof(dp));
    memset(pre, -1, sizeof(pre));
    dp[1][1] = 0;
    int pos;
    for (int i = 2; i <= n; i++) {
        for (int j = 0; j < m; j++) {
            int u = E[j].u;
            int v = E[j].v;
            int t = E[j].t;
            if (dp[i - 1][u] + t < dp[i][v]) {
                dp[i][v] = dp[i - 1][u] + t;
                pre[i][v] = u;
            }
        }
        if (dp[i][n] <= T)  pos = i;
    }
    cout << pos << endl;
    int u = n;
    while (u != -1) {
        ans.push(u);
        u = pre[pos--][u];
    }
    while (!ans.empty()){
        cout << ans.top() << " ";
        ans.pop();
    }
    return 0;
}