Codeforces_813

A.统计总时间，从总时间开始找第一个能提交的点。

#include<bits/stdc++.h>
using namespace std;

int n,m,a[1005],ok[100005] = {0};

int main()
{
    ios::sync_with_stdio(0);
    cin >> n;
    int sum = 0;
    for(int i = 1;i <= n;i++)   cin >> a[i],sum += a[i];
    cin >> m;
    for(int i = 1;i <= m;i++)
    {
        int x,y;
        cin >> x >>y;
        for(int j = x;j <= y;j++)   ok[j] = 1;
    }
    for(int i = sum;i <= 100000;i++)
    {
        if(ok[i])
        {
            cout << i << endl;
            return 0;
        }
    }
    cout << -1 << endl;
    return 0;
}

---

B.把每个unlucky值都算出来，再算最长段。

#include<bits/stdc++.h>
using namespace std;

long long x,y,l,r,a[105],b[105];

int main()
{
    ios::sync_with_stdio(0);
    cin >> x >> y >> l >> r;
    int cnt1 = 0,cnt2 = 0;
    a[++cnt1] = 1;
    b[++cnt2] = 1;
    while(a[cnt1] <= r/x)
    {
        a[cnt1+1] = a[cnt1]*x;
        cnt1++;
    }
    while(b[cnt2] <= r/y)
    {
        b[cnt2+1] = b[cnt2]*y;
        cnt2++;
    }
    set<long long> s;
    for(int i = 1;i <=cnt1;i++)
    {
        if(a[i] > r)    continue;
        for(int j = 1;j <= cnt2;j++)
        {
            if(b[j] > r) continue;
            if(a[i]+b[j] < l) continue;
            if(a[i]+b[j] > r) continue;
            s.insert(a[i]+b[j]);
        }
    }
    s.insert(l-1);
    s.insert(r+1);
    long long ans = 0;
    for(auto it = ++s.begin();it != s.end();it++)
    {
        long long xx = *it;
        it--;
        long long yy = *it;
        it++;
        ans = max(ans,xx-yy-1);
    }
    cout << ans << endl;
    return 0;
}

---

C.分两种情况，Bob一直往下跑到叶子节点或者先往上跑，再往下跑到更深的叶子节点。

#include<bits/stdc++.h>
using namespace std;

int n,x,a[200005] = {0},maxx[200005],ok[200005] = {0};
int ans;
vector<int> v[200005];

void dfs1(int now,int pre)
{
    maxx[now] = a[now];
    for(int i = 0;i < v[now].size();i++)
    {
        int t = v[now][i];
        if(t == pre)    continue;
        a[t] = a[now]+1;
        dfs1(t,now);
        if(ok[t])   ok[now] = 1;
        maxx[now] = max(maxx[now],maxx[t]);
    }
}

int main()
{
    ios::sync_with_stdio(0);
    cin >> n >> x;
    ok[x] = 1;
    for(int i = 1;i < n;i++)
    {
        int x,y;
        cin >> x >> y;
        v[x].push_back(y);
        v[y].push_back(x);
    }
    dfs1(1,-1);
    ans = maxx[x];
    for(int i = 2;i <= n;i++)
    {
        if(ok[i])
        {
            if(a[x]-a[i] < a[i])    ans = max(ans,maxx[i]);
        }
    }
    cout << ans*2 << endl;
    return 0;
}