April Fools Day Contest 2019 A. Thanos Sort

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看代码 

#include <iostream>
#include <bits/stdc++.h>
using namespace std;
#define int long long 
const int maxn=2e5+5;

int s[maxn];
signed main(){
    /*
        if the array is not sorted, snap your fingers* to remove the first or the second half of the items, and repeat the process.
        Return the maximal length of a sorted array you can obtain using Thanos sort. 
    */
    int n;cin>>n;
    for(int i=0;i<n;i++)cin>>s[i];
    
    int ans=0;
    for(int i=1;i<=n;i<<=1){//for Every len
        for(int j=0;j<n;j+=i){
            if(is_sorted(s+j,s+j+i))ans=i;//sort(s+0,s+n)  0 n-1
        }
    }
    cout<<ans<<endl;
    return 0;
}

递归：

#include <iostream>
#include <bits/stdc++.h>
using namespace std;
#define int long long 
const int maxn=2e5+5;

int s[maxn];

int maxlen(int l,int r){
    if(is_sorted(s+l,s+r+1))return r-l+1;
    return max(maxlen(l,(l+r)/2),maxlen((l+r)/2+1,r));
}
signed main(){
    /*
        if the array is not sorted, snap your fingers* to remove the first or the second half of the items, and repeat the process.
        Return the maximal length of a sorted array you can obtain using Thanos sort. 
    */
    int n;cin>>n;
    for(int i=1;i<=n;i++)cin>>s[i];
    int ans=maxlen(1,n);
    cout<<ans<<endl;
    return 0;
}