CF-1020-D. Flower Boy · znzryb

## 思路讲解

preA配合sufA，寻找最优插值位置

## AC代码



::: 源代码

```cpp
// Problem: D. Flower Boy
// Contest: Codeforces - Codeforces Round 1020 (Div. 3)
// URL: https://codeforces.com/contest/2106/problem/D
// Memory Limit: 256 MB
// Time Limit: 2000 ms
// by znzryb
// 
// Powered by CP Editor (https://cpeditor.org)

#include <bits/stdc++.h>
#define all(x) x.begin(),x.end()
#define CLR(i,a) memset(i,a,sizeof(i))
#define fi first
#define se second
#define pb push_back
#define SZ(a) ((int) a.size())
#define FOR(i, a, b) for (int i = (a); i <= (b); ++i)
#define ROF(i, a, b) for (int i = (a); i >= (b); --i)

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef __int128 i128;
typedef pair<ll,ll> pll;
typedef array<ll,3> arr;
typedef double DB;
typedef pair<DB,DB> pdd;
typedef pair<ll,bool> plb;
constexpr ll MAXN=static_cast<ll>(2e5)+10,INF=static_cast<ll>(5e18)+3;
constexpr ll mod=static_cast<ll>(1e9)+7;

ll N,M,T,A[MAXN],B[MAXN],sufA[MAXN],preA[MAXN];

inline void solve(){
	cin>>N>>M;
	FOR(i,0,N+5){
		sufA[i]=0;
		preA[i]=0;
	}
	FOR(i,1,N){
		cin>>A[i];
	}
	deque<ll> q;
	FOR(i,1,M){
		cin>>B[i];
		q.pb(B[i]);
	}
	ll idx=0;
	FOR(i,1,N){
		if(q.empty()) break;
		if(A[i]>=q.front()) q.pop_front(),++idx;
		preA[i]=idx;
	}
	if(q.empty()){
		cout<<0<<"\n";
		return;
	}
	q.clear();
	FOR(i,1,M){
		q.pb(B[i]);
	}
	idx=0;
	ROF(i,N,1){
		if(A[i]>=q.back()){
			q.pop_back();
			++idx;
		}
		sufA[i]=idx;
	}
	
#ifdef LOCAL
    FOR(i,1,N){
    	cerr<<sufA[i]<<" ";
    }
    cerr<<"\n";
    FOR(i,1,N){
    	cerr<<preA[i]<<" ";
    }
    cerr<<"\n\n";
#endif

	ll ans=INF;
	bool haveAns=false;
	FOR(i,0,N){
		if(sufA[i+1]+preA[i]==M-1){
			ans=min(ans,B[preA[i]+1]);
			haveAns=true;
		}
	}
	if(!haveAns){
		cout<<-1<<"\n";
		return;
	}
	cout<<ans<<"\n";
}

int main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);cout.tie(0);
	cin>>T;
	while(T--){
		solve();
	}
	// solve();
	return 0;
}
/*
1
4 4
1 1 3 3
1 2 3 6
AC https://codeforces.com/contest/2106/submission/317145066
*/
```


:::


## 心路历程（WA，TLE，MLE……）