2022年13th蓝桥杯C++A组 J题

题目

代码(正确性未知)

#include <bits/stdc++.h>
using namespace std;
typedef long long LL;
typedef pair<int, int> PII;
typedef pair<double, double> PDD;
int dx[] = {-1, 1, 0, 0}, dy[] = {0, 0, -1, 1};
const double eps = 1e-8;
const int N = 1e5 + 10, M = 2 * N;
int n, m, q;
int h[N], e[M], ne[M], idx;
LL w[M];
bool st[N];

unordered_map<int, LL> S;
int p[N];

void add(int a, int b, LL c)
{
    e[idx] = b;
    ne[idx] = h[a];
    w[idx] = c;
    h[a] = idx++;
}

int find(int x)
{
    if (p[x] != x)
        p[x] = find(p[x]);
    return p[x];
}

void bfs(int u)
{
    S[u] = 0;
    st[u] = true;
    queue<int> q;
    q.push(u);

    while (q.size())
    {
        int t = q.front();
        q.pop();

        for (int i = h[t]; i != -1; i = ne[i])
        {
            int j = e[i];
            if (!st[j])
            {
                st[j] = true;
                S[j] = S[t] + w[i];
                q.push(j);
            }
        }
    }
}

int main()
{
    ios::sync_with_stdio(false);
    cin.tie(0);
    memset(h, -1, sizeof h);

    cin >> n >> m >> q;
    for (int i = 0; i <= n; i++)
    {
        p[i] = i;
    }
    while (m--)
    {
        int a, b;
        LL c;
        cin >> a >> b >> c;

        // b - (a - 1) = c
        add(a - 1, b, c);
        add(b, a - 1, -c);

        int pa = find(a - 1), pb = find(b);
        if (pa != pb)
            p[pa] = pb;
    }

    for (int i = 0; i <= n; i++)
    {
        if (!st[i])
            bfs(i);
    }

    while (q--)
    {
        int l, r;
        cin >> l >> r;
        if (find(l - 1) != find(r))
            cout << "UNKNOWN\n";
        else
        {
            cout << S[r] - S[l - 1] << '\n';
        }
    }
    return 0;
}