Largest Rectangle in Histogram

Largest Rectangle in Histogram

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Given n non-negative integers representing the histogram's bar height where the width of each bar is 1, find the area of largest rectangle in the histogram.

Above is a histogram where width of each bar is 1, given height = [2,1,5,6,2,3].

The largest rectangle is shown in the shaded area, which has area = 10 unit.

For example,
Given height = [2,1,5,6,2,3],
return 10.

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public class Solution {
         public int largestRectangleArea(int[] height) {
        int [] leftSmall = new int[height.length];
        int [] rightSmall = new int[height.length];
        Stack<PositionNode> smallStack = new Stack<PositionNode>();
        for (int i = 0; i < height.length; i++) {
            while (!smallStack.isEmpty() && smallStack.peek().height >= height[i]){
                smallStack.pop();
            }
            if (!smallStack.isEmpty()) 
            {
                leftSmall[i] = smallStack.peek().pos;
             }  else {
                leftSmall[i] = -1;
             }
            smallStack.push(new PositionNode(i,height[i]));
        }
            smallStack.clear();
          for (int i = height.length - 1; i > -1; i--) {
              while (!smallStack.isEmpty() && smallStack.peek().height >= height[i]){
                smallStack.pop();
            }
            if (!smallStack.isEmpty()) {
                rightSmall[i] = smallStack.peek().pos;
            }
             else {
                 rightSmall[i] = height.length ;
             }
            PositionNode newNode = new PositionNode(i,height[i]);
            smallStack.push(newNode);
        }
        int maxArea = 0;
        for (int i = 0; i < height.length; i++) {
            int thisArea = height[i] * Math.abs(rightSmall[i] - leftSmall[i] - 1);
            maxArea = Math.max(maxArea,thisArea);
        }
        return maxArea;
    }
    class PositionNode {
        int pos;
        int height;
        public PositionNode(int pos, int height) {
            this.pos = pos;
            this.height = height;
        }
    }
}

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