@[JoshuaZheng](/user/654164) 给你一组hack:
输入
```
3
2 1 2
```
输出
```
2
```
你的输出是 3
by ssxvngn @ 2022-05-17 21:42:18
@[JoshuaZheng](/user/654164) 你的DP应该是i~j全部合成的，就不能用` dp[i][j] = max(dp[i][j], max(dp[i][k], dp[k + 1][j]));`，这样不是完全合并。
改了一下：
```cpp
#include<bits/stdc++.h>
using namespace std;
#define fr(i, a, b) for (int i = a; i <= b; i++)
typedef long long ll;
typedef unsigned long long ull;
typedef double dou;
typedef pair<int, int> pii;
const int maxn=250;
const ll inf = 1e9 + 5;
const ll mod = 1e9 + 7;
int num[maxn];
int dp[maxn][maxn],ans=-1;//ans记录
void solve(){
int n;
cin >> n;
for (int i = 1; i <= n;i++)
{
cin >> num[i];
dp[i][i] = num[i];
ans=max(ans,num[i]);//记录
}
for (int len = 1; len < n;len++)
{
for (int i = 1; i+len <= n; i++)
{
int j = i + len;
for (int k = i; k < i + len&&k<j;k++)
{
//cout << k + 1 << ' ' << j << ' ' << dp[i][k] << ' ' << dp[k + 1][j] << endl;
if(dp[i][k]==dp[k+1][j]){
dp[i][j] = max(dp[i][j], dp[i][k] + 1);
ans=max(dp[i][j],ans);
}//只要完全合并
}
}
}
cout << ans << endl;
}
int main()
{
ios::sync_with_stdio(false);
int t=1;
//cin >> t;
//t = 1;
while(t--)
{
solve();
}
system("pause");
return 0;
}
```
by ssxvngn @ 2022-05-17 21:45:12
@[一个pupil](/user/500205) 哦哦哦，好的好的，非常感谢！！！
by JoshuaZheng @ 2022-05-18 20:26:35
@[lhzawa](/user/500205) 谢谢帮助，我也卡这里了
by incomprehen @ 2022-11-08 16:41:33