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Almost Sorted Array

Time Limit: 4000/2000 MS (Java/Others) Memory Limit: 262144/262144 K (Java/Others)
Total Submission(s): 8541 Accepted Submission(s): 1982

Problem Description We are all familiar with sorting algorithms: quick sort, merge sort, heap sort, insertion sort, selection sort, bubble sort, etc. But sometimes it is an overkill to use these algorithms for an almost sorted array.

We say an array is sorted if its elements are in non-decreasing order or non-increasing order. We say an array is almost sorted if we can remove exactly one element from it, and the remaining array is sorted. Now you are given an array a1,a2,…,an

, is it almost sorted?

Input The first line contains an integer T indicating the total number of test cases. Each test case starts with an integer n in one line, then one line with n integers a1,a2,…,an.

1≤T≤2000
2≤n≤105
1≤ai≤105
There are at most 20 test cases with n>1000

Output For each test case, please output "`YES`" if it is almost sorted. Otherwise, output "`NO`" (both without quotes).

Sample Input 3 3 2 1 7 3 3 2 1 5 3 1 4 1 5

Sample Output YES YES NO
題目大意： 給你一個數列，請你判斷是不是almost sorted了。almost sorted意味著，從該數列中最多拿走一個數，這個數列就變成有序的了。 水題。 有一些坑點吧。要考慮仔細了。 拿判斷是否上升almost sorted來說。最多只能有一個下降的點。比方說a[i]<a[i-1]，這時候有兩種刪點的可能，一種是a[i]，一種是a[i-1]。兩種只要一種滿足就行。

#include<cstdio>
#include
 
<cstring>
#include<algorithm>

using namespace std;

const int maxn=100000;

int a[maxn+5];

int main()
{
    int t;
    scanf("%d",&t);
    while(t--)
    {
        int n;
        scanf("%d",&n);
        for(int i=1;i<=n;i++)
            scanf("%d",a+i);

        bool flag1=true,flag2=true;

        for(int i=2,j=0;i<=n;i++)
        {
            if(a[i]<a[i-1])
                j++;
            if(j==2)
            {
                flag1=false;
                break;
            }
        }
        if(flag1)
        {
            for(int i=2;i<=n;i++)
            {
                if(a[i]<a[i-1])
                {
                    if(i!=n&&a[i+1]<a[i-1]&&i-1!=1&&a[i-2]>a[i])
                        flag1=false;
                    break;
                }
            }
        }

        for(int i=2,j=0;i<=n;i++)
        {
            if(a[i]>a[i-1])
                j++;
            if(j==2)
            {
                flag2=false;
                break;
            }
        }
        if(flag2)
        {
            for(int i=2;i<=n;i++)
            {
                if(a[i]>a[i-1])
                {
                    if(i!=n&&a[i+1]>a[i-1]&&i-1!=1&&a[i-2]<a[i])
                        flag2=false;
                    break;
                }
            }
        }

        if(flag1||flag2)
            printf("YES\n");
        else
            printf("NO\n");
    }
    return 0;
}

View Code

hdu 5532 Almost Sorted Array (水題)