Maximize the rectangular area under Histogram

Question

I have a histogram with integer heights and constant width 1. I want to maximize the rectangular area under a histogram. e.g.:

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Answer 1

You can use O(n) method which uses stack to calculate the maximum area under the histogram.

long long histogramArea(vector &histo){
   stack s;
   long long maxArea=0;
   long long area= 0;
   int i =0;
   for (i = 0; i < histo.size();) {
    if(s.empty() || histo[s.top()] <= histo[i]){
        s.push(i++);
    }
    else{
        int top = s.top(); s.pop();
        area= histo[top]* (s.empty()?i:i-s.top()-1);
        if(area >maxArea)
            maxArea= area;
    }
  }
  while(!s.empty()){
    int top = s.top();s.pop();
    area= histo[top]* (s.empty()?i:i-s.top()-1);
    if(area >maxArea)
        maxArea= area;
 }
 return maxArea;
}

For explanation you can read here http://www.geeksforgeeks.org/largest-rectangle-under-histogram/