CCF 201712-4 90分

90分，不知道错在哪里了，dijkstra算法，用一个数组的d[i]表示以i点结尾的小路的长度，以i点为中心扩展时，若下一点为k，如果i->k是小路，则

d[j] = d[k]+M[k][j];dist[j] = min_ - pow(d[k], 2) + pow(d[j], 2);

否则直接加路径长度即可，同时把d[j]=0

#include <iostream>
#include <cstdio>
#include <climits>
#include <cmath>
#include <cstring>
#include <algorithm>
using namespace std;
const int INF = 100000000;
const int MAXN = 505;
int M[MAXN][MAXN];
int kind[MAXN][MAXN];
int dijkstra(int n)
{
    int flag[MAXN];
    long long dist[MAXN];
    int k;
    int d[MAXN];
    memset(flag, 0, sizeof(flag));
    memset(d, 0, sizeof(d));
    for (int i = 0; i < n; i++)
    {
        if (M[0][i] > 0)
        {
            if (kind[0][i] == 0)
                dist[i] = M[0][i];
            else
            {
                dist[i] = pow(M[0][i], 2);
                d[i] = M[0][i];
            }
        }
        else
            dist[i] = -1;

    }
    flag[0] = 1;
    dist[0] = 0;
    for (int i = 1; i < n; i++)
    {
        int min_ = INF;
        for (int j = 0; j < n; j++)
        {
            if (!flag[j]&&dist[j]>0&&dist[j]<min_)
            {
                min_ = dist[j];
                k = j;
            }
        }
        flag[k] = 1;
        for (int j = 0; j < n; j++)
        {
            if (!flag[j] && M[j][k]>0)
            {
                if (dist[j] < 0)
                {
                    if (kind[k][j] == 0)
                    {
                        d[j] = 0;
                        dist[j] = min_ + M[j][k];
                    }
                    else
                    {
                        d[j] = d[k]+M[j][k];
                        dist[j] = min_ - pow(d[k], 2) + pow(d[k] + M[j][k],2);
                    }
                    continue;
                }
                if (dist[j] > 0)
                {
                    if (kind[k][j] == 0)
                    {
                        if (dist[j] > min_ + M[j][k])
                        {
                            dist[j] = min_ + M[j][k];
                            d[j] = 0;
                        }
                    }
                    else
                    {
                        int temp = min_ - pow(d[k], 2) + pow(d[k] + M[k][j], 2);
                        if (dist[j] > (min_ - pow(d[k], 2) + pow(d[k]+M[k][j], 2)))
                        {
                            d[j] = d[k]+M[k][j];
                            dist[j] = min_ - pow(d[k], 2) + pow(d[j], 2);
                        }
                    }
                    continue;
                }
            }
        }

    }
    return dist[n-1];
}
int main()
{
    int n, m;
    while (~scanf("%d %d",&n,&m))
    {
        for (int i = 0; i < n; i++)
            for (int j = 0; j < n; j++)
                if (i == j)M[i][j] = 0;
                else M[i][j] = -1;
        memset(kind, 0, sizeof(kind));
        for (int i = 0; i < m; i++)
        {
            int k, a, b, c;
            scanf("%d %d %d %d", &k, &a, &b, &c);
            M[a-1][b-1] = M[b-1][a-1] = c;
            kind[a-1][b-1] = kind[b-1][a-1] = k;
        }
        cout<<dijkstra(n)<<endl;

    }
    return 0;
}

原文地址：https://www.cnblogs.com/l-h-x/p/8496821.html