POJ3249Test for Job

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <vector>
#include <cstring>
#include <queue>
#include <cmath>
using namespace std;
const int INF = 0x3fffffff;
const int maxn = 100010;
void work();

int n, m;
int val[maxn];
vector<int> g[maxn];
int du[maxn];
int d[maxn];

int main()
{
    int s, t;
    while(scanf("%d%d", &n, &m)!=EOF) {
        for(int i = 1; i <= n; i++) g[i].clear();
        memset(du, 0, sizeof(du)); // in degree.
        for(int i = 1; i <= n; i++) {
            scanf("%d", &val[i]);
            d[i] = val[i];   // init.
        }
        for(int i = 1; i <= m; i++) {
            scanf("%d%d", &s, &t);
            g[s].push_back(t);
            du[t]++;
        }
        work();
    }
    return 0;
}

queue<int> que;
bool f[maxn]; // first.
void work() {
    while(!que.empty()) que.pop();
    memset(f, false, sizeof(f));
    for(int i = 1; i <= n; i++) {
        if(du[i]==0) {
            que.push(i);
            f[i] = true;
        }
    }
    while(!que.empty()) {
        int u = que.front();
        que.pop();
        for(int i = 0; i < (int)g[u].size(); i++) {
            int v = g[u][i];
            if(f[v]==false && f[u]==true) { // first.
                d[v] = d[u]+val[v];
                f[v] = true;
            }
            if(f[v]==true && f[u]==true) {
                d[v] = max(d[v], d[u]+val[v]);
            }
            du[v]--;
            if(du[v]==0) que.push(v);
        }
    }
    int ans = -INF;
    for(int i = 1; i <= n; i++) {
        int len = (int)g[i].size();
        if(len==0) {
            ans = max(ans, d[i]);
        }
    }
    printf("%d\n", ans);
}

记忆化搜索

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <vector>
#include <cstring>
#include <queue>
#include <cmath>
using namespace std;
const int INF = 0x3fffffff;
const int maxn = 100010;

int val[maxn];
vector<int> g[maxn];
int d[maxn];
bool vis[maxn];
vector<int> start;
vector<int> des;
int du[maxn];
int n, m;
int s, t;

int dfs(int v) {
    if(vis[v]) return d[v];
    int ans = -INF;
    for(int i = 0; i < (int)g[v].size(); i++) {
        int tmp = dfs(g[v][i]);
        ans = max(ans, tmp);
    }
    vis[v] = true;
    d[v] = ans + val[v];
    return d[v];
}

void init() {
    memset(vis, false, sizeof(vis));
    for(int i = 1; i <= n; i++) {
        d[i] = -INF;
    }
    for(int i = 1; i <= n; i++) {
        if(du[i]==0) start.push_back(i);
    }
    for(int i = 1; i <= n; i++) {
        int k = (int)g[i].size();
        if(k==0) des.push_back(i);
    }
    for(int i = 0; i < (int)des.size(); i++) {
        int v = des[i];
        d[v] = val[v];
        vis[v] = true;
    }
}

int main()
{
    while(scanf("%d%d", &n, &m)!=EOF) {
        for(int i = 1; i <= n; i++) g[i].clear();
        start.clear();
        des.clear();
        memset(du, 0, sizeof(du));
        for(int i = 1; i <= n; i++) {
            scanf("%d", &val[i]);
        }
        for(int i = 1; i <= m; i++) {
            scanf("%d%d", &s, &t);
            g[s].push_back(t);
            du[t]++;
        }
        init();
        int ans = -INF;
        for(int i = 0; i < (int)start.size(); i++) {
            ans = max(ans, dfs(start[i]));
        }
        printf("%d\n", ans);
    }
    return 0;
}

POJ3249Test for Job,布布扣,bubuko.com

POJ3249Test for Job

原文：http://blog.csdn.net/achiberx/article/details/23520119