cf 153.div2 B. Unsorting Array

  B. Unsorting Array

      最近写题目越来越少了，以至于这种简单题都会错……比赛的时候写了个n^2的算法，果断超时，赛后加了个剪枝，78ms

      但是其实因为只要把有序序列中的连续不相等的两项交换，即可使之无序……所以o(n)就够了

o(n^2)

/*
author:jxy
lang:C/C++
university:China,Xidian University
**If you need to reprint,please indicate the source**
*/
#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
#define INF 1E9
using namespace std;
int a[100005],b[100005],c[100005];
bool cmp(int a,int b)
{
    return a>b;
}
int main()
{
    int n;
    scanf("%d",&n);
    if(n<=2){cout<<-1<<endl;return 0;}
    int j,i;
    for(i=0;i<n;i++)
    {
        scanf("%d",&a[i]);
        b[i]=c[i]=a[i];
    }
    sort(b,b+n);
    if(b[0]==b[n-1]){cout<<-1<<endl;return 0;}
    sort(c,c+n,cmp);
    for(i=0;i<n;i++)
    {
      if(a[i]==a[i+1])continue;
      for(j=i+1;j<n;j++)
      {
          if(a[j]==a[j-1])continue;
          if(a[i]==a[j])continue;
          if((a[j]!=b[i]||a[i]!=b[j])&&(a[i]!=c[j]||a[j]!=c[i]))
          {
              cout<<i+1<<" "<<j+1<<endl;
              return 0;
          }
      }
    }
    cout<<-1<<endl;
    return 0;
}

o(n)

#include <cstdlib>
#include <cstdio>
#include <algorithm>
using namespace std;
int f[111111],n,i;
main()
{
    scanf("%d",&n);
    for(i=1; i<=n; i++)scanf("%d",&f[i]);
    for(i=2; i<=n; i++)if(f[i] != f[i-1])
    {
        swap(f[i],f[i-1]);
        bool ok1 = true,ok2 = true;
        for(int j=2; j<=n; j++)
        {
            if(f[j-1]>f[j])ok1 = false;
            if(f[j-1]<f[j])ok2 = false;
            if(ok1 || ok2)continue;
            printf("%d %d",i-1,i);
            return 0;
        }
        swap(f[i],f[i-1]);
    }
    puts("-1");
    return 0;
}