START195B——String Deletions（注意前导一致和后导一致）（01字符串） · znzryb

## 思路讲解

可以看提交链接

## AC代码

[https://www.codechef.com/viewsolution/1173432221](https://www.codechef.com/viewsolution/1173432221)



::: 源代码

```cpp
// Problem: String Deletions
// Contest: CodeChef - START195B
// URL: https://www.codechef.com/START195B/problems/STRDEL7
// Memory Limit: 256 MB
// Time Limit: 1000 ms
// 
// Powered by CP Editor (https://cpeditor.org)

#include <bits/stdc++.h>
#define all(vec) vec.begin(),vec.end()
#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)
#define debug(var) cerr << #var <<":"<<var<<"\n";
#define lson(var) (var<<1)
#define rson(var) ((var<<1)+1)
#define V vector

using namespace std;

using  ll = long long;using ull = unsigned long long;
using DB=double;using LD=long double;
// using i128 = __int128;
using pdd = pair<DB,DB>;using plb = pair<ll,bool>;
using pll = pair<ll,ll>;using vll=vector<ll>;
using arr3 = array<ll,3> ;using arr2 = array<ll,2>;
constexpr ll MAXN=static_cast<ll>(1e6)+10,INF=static_cast<ll>(1e17)+9; // 1e18+9也是素数
constexpr ll MAXM=(ll)1e6+10;constexpr ll MAXV=(ll)1e6+10;
constexpr ll mod=static_cast<ll>(1e9)+7;
constexpr double eps=1e-8;const double pi=acos(-1.0);

ll N,M,Q,X,K,T,lT;
/*

*/
char S[MAXN];
inline void __(){
	cin>>N;
	
	FOR(i,1,N){
		cin>>S[i];
		// ++cnt[S[i]-'0'];
	}
	vector<vector<ll> > g(4);
	vll wp;
	ll dec=0;
	FOR(i,1,N){
		if(g[S[i]-'0'].empty() || i-g[S[i]-'0'].back()>1){
			wp.pb(i);
		}else{
			++dec;
// #ifdef LOCAL
    // debug(i);
    // debug(i-g[S[i]-'0'].back());
    // debug(S[i]);
    // debug(g[S[i]-'0'].back());
// #endif
		}
		g[S[i]-'0'].pb(i);
	}
	if(SZ(g[0])==N || SZ(g[1])==N){
		cout<<N<<"\n";
		return;
	}
	ll ans=N-dec;
	if(SZ(wp)>=3){
		vll cnt(4,0);
		ll lans=0;
		if(S[wp.back()]!=S[wp.front()]){
			lans=SZ(wp)-3;
		}else{
			lans=SZ(wp)-2;
		}
		ans-=lans;
	}
	ROF(i,N,1){
		if(S[i]==S[N]){
			++ans;
		}else{
			break;
		}
	}
	FOR(i,1,N){
		if(S[i]==S[1]){
			++ans;
		}else{
			break;
		}
	}
	ans-=1;
	ans-=1;
	cout<<ans<<"\n";
}

int main()
{
	ios::sync_with_stdio(false);
	cin.tie(0);cout.tie(0);
	
	cin>>lT;
	while(lT--)
		__();
	return 0;
}
/*
AC
https://www.codechef.com/viewsolution/1173432221
1
5
11010
4

1
5
01010

ans:2
*/
```


:::


## 心路历程（WA，TLE，MLE……）