Codeforces #831A: Unimodal Array 题解

这题很容易写错

先从左往右扫，找到不再上升的点

然后跳过中间的那些平着的点

最后看剩下的是否下降

要注意的是，下降部分的第一个要小于平台

#include <cstdio>#include <iostream>#include <cstring>#include <string>#include <cmath>#include <algorithm>#include <cstdlib>#include <utility>#include <map>#include <stack>#include <set>#include <vector>#include <queue>#include <deque>#include <bitset>#define x first#define y second#define mp make_pair#define pb push_back#define LL long long#define Pair pair<int,int>#define LOWBIT(x) x & (-x)using namespace std;const int zero_stand=1500;const int MOD=1e9+7;const int INF=0x7ffffff;const int magic=348;int n;int a[101];int main (){int i;scanf("%d",&n);for (i=1;i<=n;i++) scanf("%d",&a[i]);if (n==1 || n==2){printf("YES\n");return 0;}int pos=1;while (pos<=n-1 && a[pos]<a[pos+1]) pos++;while (pos<=n-1 && a[pos]==a[pos+1]) pos++;for (i=pos;i<=n-1;i++) if (a[i]<=a[i+1]){printf("NO\n");return 0;}printf("YES\n");return 0;}