【leetcode】Largest Rectangle in Histogram

#include<iostream>
#include<vector>
using namespace std;
class Solution
{
public:
int fun(vector<int> a)
{

int i;
int maxlength=0;
for( i=0;i<a.size();i++)
{
int j=i+1;
for(;j<a.size();j++)
{
if(a[j]<a[j-1])
{
i=j-1;
cout<<i<<endl;
break;
}
else
i=j;
}
int low=a[i];
for(int k=i;k>=0;k--)
{
if(a[k]<low)
low=a[k];
if(maxlength<(i-k+1)*low)
maxlength=(i-k+1)*low;
}
}
return maxlength;
}
};

void main()
{
Solution solution;
int arr[10]={2,1,5,6,5,2,3};
vector<int>a(arr,arr+6);
cout<<solution.fun(a);
}