hdu 5532（最长上升子序列）

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

332 1 733 2 153 1 4 1 5

 

Sample Output

YESYESNO

题意：给你一组数，能否删除一个后使他成为升序或者降序

思路：

正反分别求一次最长上升子序列，只要长度有一次≥n-1即可

#include <iostream>#include <cstdio>#include <cstring>#include <cstdlib>#include <queue>#include <vector>#include <algorithm>#include <functional>typedef long long ll;using namespace std;const int maxn = 1e5 + 5;int b[maxn];int n;int Search(int num,int low,int high){    int mid;    while(low <= high)    {        mid = (low+high)/2;        if(num >= b[mid])            low= mid+1;        else            high = mid-1;    }    return low;}int fin(int *a){    int len,pos;    b[1] = a[1];    len = 1;    for(int i = 2;i <= n;i++)    {        if(a[i] >= b[len])        {            len = len+1;            b[len] = a[i];        }        else        {            pos = Search(a[i],1,len);            b[pos ]  = a[i];        }    }    if(len >= n-1)        return true;    else        return false;}int t[maxn],tt[maxn];int main(){    int cas;    scanf("%d",&cas);    while(cas--)    {        scanf("%d",&n);        for(int i = 1;i <= n;i++)            scanf("%d",t+i);        for(int i = 1;i <= n;i++)            tt[n+1-i] = t[i];        bool flag = fin(t);        flag |= fin(tt);        if(flag)            printf("YES\n");        else            printf("NO\n");    }}