G - MPI Maelstrom

#include<algorithm>  //SPFA
#include<queue>
#include<stdio.h>
#include<string.h>
#include<vector>
using namespace std;

const int maxn = 105;
const int INF = 0xfffffff;

struct node
{
    int y, time;
    node(int y, int t):y(y), time(t){}
};
vector<node> G[maxn];       //G[i][j] 从i到G[i][j].y 的时间为G[i][j].time
int v[maxn];

void spfa(int s)
{
    queue<int> Q;
    Q.push(s);

    while(Q.size())
    {
        s = Q.front();Q.pop();
        int len = G[s].size();

        for(int i=0; i<len; i++)
        {
            node q = G[s][i];
            if(v[q.y] > v[s]+q.time)
            {
                v[q.y] = v[s] + q.time;
                Q.push(q.y);
            }
        }
    }
}

int main()
{
    int N;

    while(scanf("%d", &N) != EOF)
    {
        int i, j, x;
        char s[30];

        for(i=1; i<=N; i++)
        {
            v[i] = INF;
            G[i].clear();
        }
        v[1] = 0;

        for(i=2; i<=N; i++)
        for(j=1; j<i; j++)
        {
            scanf("%s", s);
            if(s[0] != 'x')
            {
                sscanf(s, "%d", &x);
                G[i].push_back(node(j, x));
                G[j].push_back(node(i, x));
            }
        }

        spfa(1);

        int ans = -INF;

        for(i=1; i<=N; i++)
            ans = max(ans, v[i]);

        printf("%d\n", ans);
    }

    return 0;
}