Codeforces 459E Pashmak and Graph(dp+贪心)

题目链接：Codeforces 459E Pashmak and Graph

题目大意：给定一张有向图，每条边有它的权值，要求选定一条路线，保证所经过的边权值严格递增，输出最长路径。

解题思路：将边按照权值排序，每次将相同权值的边同时加入，维护每个点作为终止点的最大长度即可。

#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;

const int maxn = 3 * 1e5+5;

struct edge {
    int u, v, w;
}s[maxn];

bool cmp (const edge& a, const edge& b) {
    return a.w < b.w;
}

int n, m, d[maxn], f[maxn], val[maxn];

int main () {
    scanf("%d%d", &n, &m);
    memset(d, 0, sizeof(d));
    memset(f, 0, sizeof(f));
    memset(val, 0, sizeof(val));

    for (int i = 0; i < m; i++)
        scanf("%d%d%d", &s[i].u, &s[i].v, &s[i].w);
    sort(s, s + m, cmp);

    for (int i = 0; i < m; i++) {

        int j;
        for (j = i; s[j].w == s[i].w && j < m; j++);

        for (int k = i; k < j; k++)
            d[s[k].v] = max(d[s[k].v], f[s[k].u] + 1);
        for (int k = i; k < j; k++)
            f[s[k].v] = d[s[k].v];
        i = j - 1;
    }

    int ans = 0;
    for (int i = 1; i <= n; i++)
        ans = max(ans, f[i]);
    printf("%d\n", ans);
    return 0;
}