Codeforces Round 875 (Div. 2)

Codeforces Round 875 (Div. 2)

A - Twin Permutations

思路：让序列全相等为n+1即可

#include<bits/stdc++.h>
using namespace std;
typedef pair<int,int>PII;

typedef pair<string,int>PSI;
typedef pair<string,string>PSS;
const int N=2e5+5,INF=0x3f3f3f3f,Mod=1e9+7;

const double eps=1e-6;
typedef long long ll;
//#define int long long



void solve(){
    int n;cin>>n;
    for(int i=1,x;i<=n;++i){
        cin>>x;
        cout<<1+n-x<<' ';
    }cout<<'\n';
}
int32_t main(){
    ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);
    int t=1;
    cin>>t;
    while(t--){
        solve();
    }
    return 0;
}

B - Array merging

思路：分别求序列中最长连续长度，不同序列中相同数字的可以相加

#include<bits/stdc++.h>
using namespace std;
typedef pair<int,int>PII;

typedef pair<string,int>PSI;
typedef pair<string,string>PSS;
const int N=2e5+5,INF=0x3f3f3f3f,Mod=1e9+7;

const double eps=1e-6;
typedef long long ll;
//#define int long long



void solve(){
    int n;cin>>n;
    map<int,int>mp,mmp;
    for(int i=1,x,l,c=1;i<=n;++i){
        cin>>x;
        if(i==1)l=x;
        else if(l!=x)mp[l]=max(mp[l],c),c=1,l=x;
        else c++;
        if(i==n)mp[l]=max(mp[l],c);
    }
    for(int i=1,x,l,c=1;i<=n;++i){
        cin>>x;
        if(i==1)l=x;
        else if(l!=x)mmp[l]=max(mmp[l],c),c=1,l=x;
        else c++;
        if(i==n)mmp[l]=max(mmp[l],c);
    }
    int ma=0;
    for(auto v:mp){
        ma=max(ma,v.second+mmp[v.first]);
    }
    for(auto v:mmp){
        ma=max(ma,v.second+mp[v.first]);
    }
    cout<<ma<<'\n';
}
int32_t main(){
    ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);
    int t=1;
    cin>>t;
    while(t--){
        solve();
    }
    return 0;
}

C - Copil Copac Draws Trees

思路：dfs或bfs或dp。从1开始，遍历每条边w，若当前边在w前，则w与当前边在同一次得到；若当前边在w后，则w在当前边的下一次得到

#include<bits/stdc++.h>
using namespace std;
typedef pair<int,int>PII;

typedef pair<string,int>PSI;
typedef pair<string,string>PSS;
const int N=5e5+5,INF=0x3f3f3f3f,Mod=1e9+7;
//#define endl '\n'
const double eps=1e-6;
typedef long long ll;
//#define int long long


void solve(){
    int n,ans=1;cin>>n;
    vector<PII>ve[n+1];
    vector<bool>st(n+1,false);
    for(int i=0,u,v;i<n-1;++i){
        cin>>u>>v;
        ve[u].push_back({v,i});
        ve[v].push_back({u,i});
    }
    function<void(int,int,int)> dfs=[&](int u,int pos,int feet){
        for(auto v:ve[u]){
            if(st[v.first])continue;
            st[v.first]=true;
            if(v.second<pos){
                ans=max(ans,feet+1);
                dfs(v.first,v.second,feet+1);
            }else{
                ans=max(ans,feet);
                dfs(v.first,v.second,feet);
            }
        }
    };
    st[1]=true;
    dfs(1,0,1);
    cout<<ans<<'\n';
}
int main(){
    ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);
    int t=1;
    cin>>t;
    while(t--){
        solve();
    }
    return 0;
}

#include<bits/stdc++.h>
using namespace std;
typedef pair<int,int>PII;

typedef pair<string,int>PSI;
typedef pair<string,string>PSS;
const int N=5e5+5,INF=0x3f3f3f3f,Mod=1e9+7;
//#define endl '\n'
const double eps=1e-6;
typedef long long ll;
//#define int long long


void solve(){
    int n,ans=1;cin>>n;
    vector<PII>dp(n+1,{0,0}),ve[n+1];
    vector<bool>st(n+1,false);
    int p=-1;
    for(int i=1,u,v;i<n;++i){
        cin>>u>>v;
        if(u==1&&p==-1)p=i;
        if(v==1&&p==-1)p=i;
        ve[u].push_back({v,i});
        ve[v].push_back({u,i});
    }
    st[1]=true;dp[1]={1,p};
    queue<int>q;
    q.push(1);
    while(q.size()){
        int u=q.front();q.pop();
        for(auto v:ve[u]){
            if(st[v.first])continue;
            st[v.first]=true;
            q.push(v.first);
            if(v.second<dp[u].second){
                dp[v.first].first=dp[u].first+1,dp[v.first].second=v.second;
                ans=max(ans,dp[v.first].first);
            }
            else{
                dp[v.first].first=dp[u].first,dp[v.first].second=v.second;
                ans=max(ans,dp[v.first].first);
            }
        }
    }
    cout<<ans<<'\n';
}
int main(){
    ios::sync_with_stdio(0),cin.tie(0),cout.tie(0);
    int t=1;
    cin>>t;
    while(t--){
        solve();
    }
    return 0;
}