Array of integers is unimodal, if:
- it is strictly increasing in the beginning;
- after that it is constant;
- after that it is strictly decreasing.
The first block (increasing) and the last block (decreasing) may be absent. It is allowed that both of this blocks are absent.
For example, the following three arrays are unimodal: [5, 7, 11, 11, 2, 1], [4, 4, 2], [7], but the following three are not unimodal:[5, 5, 6, 6, 1], [1, 2, 1, 2], [4, 5, 5, 6].
Write a program that checks if an array is unimodal.
The first line contains integer n (1 ≤ n ≤ 100) — the number of elements in the array.
The second line contains n integers a1, a2, ..., an (1 ≤ ai ≤ 1 000) — the elements of the array.
Print "YES" if the given array is unimodal. Otherwise, print "NO".
You can output each letter in any case (upper or lower).
6
1 5 5 5 4 2
YES
5
10 20 30 20 10
YES
4
1 2 1 2
NO
7
3 3 3 3 3 3 3
YES
In the first example the array is unimodal, because it is strictly increasing in the beginning (from position 1 to position 2, inclusively), that it is constant (from position 2 to position 4, inclusively) and then it is strictly decreasing (from position 4 to position 6, inclusively).
题意:给你一个序列是否是先严格递增有一个极大值然后递减;递增和递减部分可以没有;
题解:找到出数组的最大值,然后看是否符合条件。下面给出AC代码
#include<iostream> #include<cstdio> #include<cstring> #include<algorithm> #include<vector> #include<queue> #define LL long long using namespace std; const int maxn=1e2+5; int a[maxn],n; int main() { scanf("%d ",&n); int maxl=0,id=0; for(int i=0;i<n;i++) { scanf("%d",&a[i]); if(a[i]>maxl) { id=i;maxl=a[i]; } } bool flag=true,flag2=true; if(a[0]==a[1]&&maxl>a[0]||a[n-2]==a[n-1]&&maxl>a[n-1]) { cout<<"NO "; } else { for(int i=0;i<n-1;i++) { if(a[i]<a[i+1]&&flag2) { continue; } else if(a[i]==a[i+1]&&flag2) { if(a[i]!=maxl) { flag=false;break; } continue; } else if(a[i]>a[i+1]&&flag2) { if(a[i]!=maxl) { flag=false;break; } flag2=false; } if(!flag2&&a[i]>a[i+1]) { continue; } else if(!flag2&&a[i]==a[i+1]) { if(a[i]!=maxl) { flag=false;break; } continue; } else if(!flag2&&a[i]<a[i+1]) { flag=false; //cout<<1<<endl; break; } } if(flag) { cout<<"YES "; } else { cout<<"NO "; } } }