HDU_4019 Instrction Arrangement

　Warmup for 2011 Asia Regional Chengdu (Alibaba精英赛题目重现,SJTU命题)——Problem 1009　

/*比赛没做，周六下午做zoj的月赛做的想吐，周日一点心情也没有。
今天挺师兄说这题是dp的，就做了做。其实更像拓扑排序，大题思路就是把
所有入度为0的点入栈，然后出栈。本体多组数据，WA了一晚上！妹的！*/

//My Code:

#include <iostream>
#include <cstdio>
#include <cstring>

using namespace std;

const int N = 1010;

long long pre[N][N];
int in[N], sta[N];
long long dp[N];

int main() {
    //freopen("data.in", "r", stdin);

    int n, m, top = 0;
    int x, y, z, i;
    long long max;
    while(~scanf("%d%d", &n, &m)) {

    memset(pre, 0, sizeof(pre));
    memset(dp, 0, sizeof(dp));
    memset(in, 0, sizeof(in));
    memset(sta, 0, sizeof(sta));

    while(m--) {
        scanf("%d%d%d", &x, &y, &z);
        pre[y][x] = z; in[y]++;
    }

    for(i = 0; i < n; i++)
        if(in[i] == 0) {
            dp[i] = 1; sta[top++] = i;
        }

    while(top != 0) {
        x = sta[--top];
        for(i = 0; i < n; i++) {
            if(pre[i][x] != 0) {
                dp[i] = dp[i] > pre[i][x] + dp[x] ? dp[i] : pre[i][x] + dp[x];
                in[i]--; pre[i][x] = 0;
                if(in[i] == 0)    sta[top++] = i;
            }
        }
    }

    for(max = 0, i = 0; i < n; i++) {
        max = max > dp[i] ? max : dp[i];
    }

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