LeetCode--Largest Rectangle in Histogram

 1 class Solution {
 2 public:
 3     int largestRectangleArea(vector<int> &height) {
 4         int n = height.size();
 5         if(n == 0)
 6         {
 7             return 0;
 8         }
 9         vector<int> leftMax(n);
10         vector<int> rightMax(n);
11         stack<int> s;
12         int i;
13         for(i = 0 ; i < n ; ++i)
14         {
15             leftMax[i] = 0;
16             if(i > 0)
17             {
18                 int pre = -1;
19                 while(!s.empty())
20                 {
21                     int tmp = s.top();
22                     if(height[tmp] >= height[i])
23                     {
24                         s.pop();
25                     }
26                     else
27                     {
28                         pre = tmp;
29                         break;
30                     }
31                 }
32                 s.push(i);
33                 leftMax[i] = i - pre - 1;
34             }
35             else
36             {
37                 s.push(i);
38             }
39         }
40         stack<int> s1;
41         for(i = n-1 ; i >= 0 ; --i)
42         {
43             rightMax[i] = 0;
44             if(i < n-1)
45             {
46                 int next = n;
47                 while(!s1.empty())
48                 {
49                     int tmp = s1.top();
50                     if(height[tmp] >= height[i])
51                     {
52                         s1.pop();
53                     }
54                     else
55                     {
56                         next = tmp;
57                         break;
58                     }
59                 }
60                 s1.push(i);
61                 rightMax[i] = next - i - 1;
62             }
63             else
64             {
65                 s1.push(i);
66             }
67         }
68         int res = INT_MIN;
69         for(i = 0 ; i < n ; ++i)
70         {
71             res = max(res,(leftMax[i]+rightMax[i]+1)*height[i]);
72         }
73         return res;
74     }
75 };