題意：

告訴你n 個數， 問你是否去掉k 個數後， 原序列變成非嚴格遞增序列或者非嚴格遞減序列。 

思路：

顯然求一遍LIS ， 倒過來在求一邊LIS， 比較ans 和 k 的關係即可。

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
int T;

const int maxn = 100000 + 10;

int a[maxn], c[maxn];

int main(){
    scanf("%d",&T);
    while(T--){
        int n, k;
        scanf("%d %d",&n, &k);
        for (int i = 0; i < n; ++i){
            scanf("%d", a+i);
        }

        int cnt = 0;
        int ans = 0;
        for (int i = 0; i < n; ++i){

            int p = upper_bound(c, c + cnt, a[i]) - c;
            if (p == cnt){
                c[cnt++] = a[i];
                ans = max(ans, cnt);
            }
            else {
                c[p] = a[i];
            }
        }
        cnt = 0;
        for (int i = n-1; i >= 0; --i){
            int p = upper_bound(c, c + cnt, a[i]) - c;
            if (p == cnt){
                c[cnt++] = a[i];
                ans = max(ans, cnt);
            }
            else {
                c[p] = a[i];
            }
        }
//        printf("ans = %d\n", ans);
        if (n - k <= ans){
            puts("A is a magic array.");
        }
        else {
            puts("A is not a magic array.");
        }


    }


    return 0;
}
 

array array array

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
Total Submission(s): 219    Accepted Submission(s): 131


Problem Description One day, Kaitou Kiddo had stolen a priceless diamond ring. But detective Conan blocked Kiddo's path to escape from the museum. But Kiddo didn't want to give it back. So, Kiddo asked Conan a question. If Conan could give a right answer, Kiddo would return the ring to the museum. 
Kiddo: "I have an array A

 and a number k, if you can choose exactly k elements from A and erase them, then the remaining array is in non-increasing order or non-decreasing order, we say A is a magic array. Now I want you to tell me whether A is a magic array. " Conan: "emmmmm..." Now, Conan seems to be in trouble, can you help him?

Input The first line contains an integer T indicating the total number of test cases. Each test case starts with two integers n

 and k in one line, then one line with n integers: A1,A2…An.
1≤T≤20
1≤n≤105
0≤k≤n
1≤Ai≤105

Output For each test case, please output "A is a magic array." if it is a magic array. Otherwise, output "A is not a magic array." (without quotes).

Sample Input 3 4 1 1 4 3 7 5 2 4 1 3 1 2 6 1 1 4 3 5 4 6
Sample Output A is a magic array. A is a magic array. A is not a magic array.
Source
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