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LargestRectangle.java
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LargestRectangle.java
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import java.io.*;
import java.util.*;
public class Solution {
public static int solution(int[] height) {
int n = height.length;
if(n == 0) return 0;
Stack<Integer> left = new Stack<Integer>();
Stack<Integer> right = new Stack<Integer>();
int[] width = new int[n];// widths of intervals.
Arrays.fill(width, 1);// all intervals should at least be 1 unit wide.
for(int i = 0; i < n; i++){
// count # of consecutive higher bars on the left of the (i+1)th bar
while(!left.isEmpty() && height[i] <= height[left.peek()]){
// while there are bars stored in the stack, we check the bar on the top of the stack.
left.pop();
}
if(left.isEmpty()){
// all elements on the left are larger than height[i].
width[i] += i;
} else {
// bar[left.peek()] is the closest shorter bar.
width[i] += i - left.peek() - 1;
}
left.push(i);
}
for (int i = n-1; i >=0; i--) {
while(!right.isEmpty() && height[i] <= height[right.peek()]){
right.pop();
}
if(right.isEmpty()){
// all elements to the right are larger than height[i]
width[i] += n - 1 - i;
} else {
width[i] += right.peek() - i - 1;
}
right.push(i);
}
int max = Integer.MIN_VALUE;
for(int i = 0; i < n; i++){
// find the maximum value of all rectangle areas.
max = Math.max(max, width[i] * height[i]);
}
return max;
}
public static void main(String[] args) {
Scanner in = new Scanner(System.in);
int n = in.nextInt();
int height[] = new int[n];
for (int i = 0; i < n; i++)
height[i] = in.nextInt();
System.out.println(solution(height));
}
}