没想到。。。。
参考:http://blog.youkuaiyun.com/qq_21057881/article/details/52739386
#include <iostream>
#include <algorithm>
using namespace std;
const int MAXN = 5e4+10;
int num[MAXN];
int index[MAXN];
int main()
{
int n;
cin >> n;
for(int i = 0; i < n; ++i)
{
cin >> num[i];
index[i] = i;
}
stable_sort(index,index+n,[](int a, int b)->bool {return num[a] < num[b];});
int mark = 5e4+10;
int res = 0;
for(int i = 0; i < n; ++i)
{
if(index[i] > mark) res = max(res,index[i]-mark);
else mark = index[i];
}
cout << res << endl;
return 0;
}