AtCoder Beginner Contest 137

AtCoder Beginner Contest 137

昨天还是前天写的，忘了，今天补一下
https://atcoder.jp/contests/abc137

A - +-x

#include <bits/stdc++.h>

using namespace std;

int main () {
    int a, b;
    cin >> a >> b;
    cout << max ({a + b, a - b, a * b});
}

B - One Clue

#include <bits/stdc++.h>

using namespace std;

int main () {
    int a, b;
    cin >> a >> b;
    for (int i = max(-1000000, b - a + 1);  i <= min (1000000, b + a - 1); i++)     cout << i << ' ';
}

C - Green Bin

#include <bits/stdc++.h>
#define ll long long

using namespace std;

int main () {
    int n;
    cin >> n;
    map<string, int> mp;
    while (n --) {
        string s;
        cin >> s;
        sort (s.begin (), s.end ());
        mp[s] ++;
    }
    ll ans = 0;
    for (auto i : mp) {
        n = i.second;
        ans += 1ll * n * (n - 1) / 2;
    }
    cout << ans;
}

//hash

D - Summer Vacation

贪心，堆维护

#include <bits/stdc++.h>
#define ll long long

using namespace std;
typedef pair<int, int> pii;
ll ans;

int main () {
    int n, m;
    cin >> n >> m;
    vector <pii> v;
    for (int i = 0; i < n; i++) {
        int a, b;
        cin >> a >> b;
        v.push_back ({a, b});
    }
    sort (v.begin (), v.end ());
    priority_queue <int> q;
    for (int i = 1, j = 0; i <= m; i++) {
        for (; j < n; j++) {
            if (v[j].first > i)     break;
            q.push (v[j].second);
        }
        if (!q.empty ())    ans += q.top (), q.pop ();
    }
    cout << ans << endl;
}

E - Coins Respawn

好题
图论。spfa判正环（可达n才算），求最长路。
正着spfa求最长路，建反向边判正环可达性

#include <bits/stdc++.h>
#define int long long

using namespace std;
const int N = 2505, M = 5005;
int n, m, p;
int h[N], ne[M], e[M], w[M], idx;
int d[N], dis[N], cnt[N];
bool vis[N], vis1[N];
vector <int> v[N];

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

bool spfa () {
    queue <int> q;
    memset (dis, -0x3f, sizeof dis);
    vis[1] = true;
    //cnt[1] = 1;
    dis[1] = 0;
    q.push(1);
    while(!q.empty()) {
        int u = q.front();
        q.pop();
        vis[u] = false;
        for (int i = h[u]; i != -1; i = ne[i]) {
            int v = e[i];
            if (!vis1[v])       continue;
            int ww = dis[u] + w[i];
            if(dis[v] < ww) {
                dis[v] = ww;
                if(!vis[v]) {
                    vis[v] = true;
                    cnt[v] ++;
                    if(cnt[v] > n)  return true;
                    q.push(v);
                }
            }
        }
    }
    return false;
}

void dfs (int a) {
    if (vis1[a])     return ;
    vis1[a] = true;
    for (auto b : v[a])    dfs (b);
}

signed main () {
    memset (h, -1, sizeof h);
    cin >> n >> m >> p;
    for (int i = 1; i <= m; i++) {
        int a, b, c;
        cin >> a >> b >> c;
        add (a, b, c - p);
        v[b].push_back (a); //建反向边
    }
    //有正环则无解
    dfs (n);
    if (spfa ())    cout << -1;
    else    cout << max(0ll, dis[n]) << endl;
}

F - Polynomial Construction

一个数论，暂时没懂