算法问题实战策略 NTHLON

地址 https://algospot.com/judge/problem/read/NTHLON

 

#include <iostream>
#include <vector>
#include <algorithm>
#include <queue>


using namespace std;

int V;
//图的邻接表表示法 保存成对(连接的顶点序号 边线加权值)
vector<pair<int, int>> adj[410];
const int START = 401;
const int INF = 0x3f3f3f3f;


vector<int> dijkstra(int src)
{
    vector<int > dist(V, INF);
    dist[src] = 0;
    priority_queue<pair<int, int>> pq;
    pq.push(make_pair(0, src));

    while (!pq.empty()) {
        int cost = -pq.top().first;
        int here = pq.top().second;
        pq.pop();

        if (dist[here] < cost) continue;

        for (int i = 0; i < adj[here].size(); ++i) {
            int there = adj[here][i].first;
            int nextDist = cost + adj[here][i].second;

            if (dist[there] > nextDist) {
                dist[there] = nextDist;
                pq.push(make_pair(-nextDist, there));
            }
        }
    }

    return dist;
}

//==========================================================

//返回(A国选手的预想耗时-B国家选手的预想耗时)的顶点序号
int vertex(int delta) {
    return delta + 200;
}

//a[]=A国选手的各项预想耗时
//b[]=B国选手的各项预想耗时
int solve(const vector<int>& a, const vector<int>& b) {
    //生成图结构
    V = 402;
    for (int i = 0; i < V; i++) adj[i].clear();
    for (int i = 0; i < a.size(); i++) {
        int delta = a[i] - b[i];
        adj[START].push_back(make_pair(vertex(delta), a[i]));
    }

    //当前耗时之差
    for (int delta = -200; delta <= 200; ++delta) {
        //若添加第i个比赛项目
        for (int i = 0; i < a.size(); ++i) {
            int next = delta + a[i] - b[i];
            //没有必要生成耗时之差超过200的顶点
            if (abs(next) > 200) continue;
            adj[vertex(delta)].push_back(make_pair(vertex(next), a[i]));
        }
    }

    vector<int> shortest = dijkstra(START);
    int ret = shortest[vertex(0)];
    if (ret == INF) return -1;
    return ret;
}





int main()
{
    int n,m;
    cin >> n;
    while (n--) {
        cin >> m;
        vector<int> va;
        vector<int> vb;
        for (int i = 0; i < m; i++) {
            int a, b;
            cin >> a >> b;
            va.push_back(a);
            vb.push_back(b);
        }
        int ret = solve(va, vb);
        if (ret != -1) {
            cout << ret << endl;
        }
        else {
            cout << "IMPOSSIBLE" << endl;
        }
    }


    return 0;
}