You are given an array a₁, a₂, ..., a_n consisting of n integers, and an integer k. You have to split the array into exactly k non-empty subsegments. You'll then compute the minimum integer on each subsegment, and take the maximum integer over the k

Definitions of subsegment and array splitting are given in notes.

The first line contains two integers n and k (1 ≤ k ≤ n ≤  10⁵) — the size of the array a and the number of subsegments you have to split the array to.

The second line contains n

Print single integer — the maximum possible integer you can get if you split the array into k non-empty subsegments and take maximum of minimums on the subsegments.

5 2
1 2 3 4 5

5

5 1
-4 -5 -3 -2 -1

-5

A subsegment [l,  r] (l ≤ r) of array a is the sequence a_l,  a_l + 1,  ...,  a_r.

Splitting of array a of n elements into k subsegments [l₁, r₁], [l₂, r₂], ..., [l_k, r_k] (l₁ = 1, r_k = n, l_i = r_i - 1 + 1 for all i > 1) is k sequences (a_l1, ..., a_r1), ..., (a_lk, ..., a_rk).

In the first example you should split the array into subsegments [1, 4] and [5, 5] that results in sequences (1, 2, 3, 4) and (5). The minimums are min(1, 2, 3, 4) = 1 and min(5) = 5. The resulting maximum is max(1, 5) = 5. It is obvious that you can't reach greater result.

In the second example the only option you have is to split the array into one subsegment [1, 5], that results in one sequence ( - 4,  - 5,  - 3,  - 2,  - 1). The only minimum is min( - 4,  - 5,  - 3,  - 2,  - 1) =  - 5. The resulting maximum is  - 5.

解題：k  =  1 取整個陣列最小值

           k  =  2 取陣列頭和尾的最大值  兩個區間，想要最優，從第一個和最後一個選一個最大的因為不管在哪分都不會比兩端的大
           k >=  3 取整個陣列最大的——分3段 把最大值那個單分出來

#include<cstdio>
#include<algorithm>
using namespace std;
const int INF=0x3f3f3f3f;
int num[100010];
int main()
{
	int n,k;
//	scanf("%d%d",&n,&k); 
	while(scanf("%d%d",&n,&k)!=EOF)
	{
		int minn=INF,maxx=-INF;
		for(int i = 0; i < n; i++)
		{
			scanf("%d",&num[i]);
			minn=min(minn,num[i]);
			maxx=max(maxx,num[i]);
		}
		if(k == 1)
			printf("%d\n",minn);
		if(k == 2)
			printf("%d\n",max(num[0],num[n-1]));//兩個區間，想要最優，從第一個和最後一個選一個最大的 
		if(k >= 3)							//因為不管在哪分都不會比兩端的大 
			printf("%d\n",maxx);
	}
	return 0;
}