Max. plocha obdélníku v histogramu

max. plocha obdélníku v histogramu

// C++ program to find maximum rectangular area in
// linear time
#include<bits/stdc++.h>
using namespace std;
 
// The main function to find the maximum rectangular
// area under given histogram with n bars
int getMaxArea(int hist[], int n)
{
    // Create an empty stack. The stack holds indexes
    // of hist[] array. The bars stored in stack are
    // always in increasing order of their heights.
    stack<int> s;
 
    int max_area = 0; // Initialize max area
    int tp;  // To store top of stack
    int area_with_top; // To store area with top bar
                       // as the smallest bar
 
    // Run through all bars of given histogram
    int i = 0;
    while (i < n)
    {
        // If this bar is higher than the bar on top
        // stack, push it to stack
        if (s.empty() || hist[s.top()] <= hist[i])
            s.push(i++);
 
        // If this bar is lower than top of stack,
        // then calculate area of rectangle with stack
        // top as the smallest (or minimum height) bar.
        // 'i' is 'right index' for the top and element
        // before top in stack is 'left index'
        else
        {
            tp = s.top();  // store the top index
            s.pop();  // pop the top
 
            // Calculate the area with hist[tp] stack
            // as smallest bar
            area_with_top = hist[tp] * (s.empty() ? i :
                                   i - s.top() - 1);
 
            // update max area, if needed
            if (max_area < area_with_top)
                max_area = area_with_top;
        }
    }
 
    // Now pop the remaining bars from stack and calculate
    // area with every popped bar as the smallest bar
    while (s.empty() == false)
    {
        tp = s.top();
        s.pop();
        area_with_top = hist[tp] * (s.empty() ? i :
                                i - s.top() - 1);
 
        if (max_area < area_with_top)
            max_area = area_with_top;
    }
 
    return max_area;
}
 
// Driver program to test above function
int main()
{
    int hist[] = {6, 2, 5, 4, 5, 1, 6};
    int n = sizeof(hist)/sizeof(hist[0]);
    cout << "Maximum area is " << getMaxArea(hist, n);
    return 0;
}