计算最大矩形

其实这就是LeetCode上的一道题目，再次证明了LeetCode在面试中的巨大作用。
原题参考：84. Largest Rectangle in Histogram
经过不懈努力，终于在抄抄抄的过程中把题目解出来了。

import java.util.Stack;

class Solution {
    private int max = 0;
    private Stack<Integer> stack = new Stack<>();
    public int largestRectangleArea(int[] heights) {
        int n = heights.length;
        if (heights == null || n == 0) {
            return 0;
        }
        for(int i = 0; i<n;i++){
            if (stack.isEmpty()) {
                stack.push(i);
                continue;
            }
            if(heights[i]>heights[stack.peek()]){
                stack.push(i);
                continue;
            }
            while(!stack.isEmpty() && heights[i]<heights[stack.peek()]){
                updateMax(heights,i);
            }
            stack.push(i);
        }
        while (!stack.isEmpty()) {
            updateMax(heights, heights.length);
        }
        return max;
    }

    private void updateMax(int[] heights, int right) {
        int curIndex = stack.pop();
        int h = heights[curIndex];
        // 计算边界
        // 如果栈的元素大于1，那么左边界是前一个元素下标+1
        // 如果栈的元素等于１，那么左边界就是０
        int left = stack.isEmpty()?0:stack.peek()+1;
        int w = right - left;
        int area = w * h;
        if(max<area){
            max = area;
        }
    }
}

测试代码

import org.junit.Assert;
import org.junit.Before;
import org.junit.Test;

import static org.junit.Assert.*;

public class SolutionTest {
    private Solution solution;

    @Before
    public void setUp() throws Exception {
        solution = new Solution();
    }

    @Test
    public void test_1() {
        int max = solution.largestRectangleArea(new int[]{2,1,5,6,2,3});
        Assert.assertEquals(10,max);
    }

    @Test
    public void test_2() {
        int max = solution.largestRectangleArea(new int[]{2,1});
        Assert.assertEquals(2,max);
    }

    @Test
    public void test_3() {
        int max = solution.largestRectangleArea(new int[]{1,2});
        Assert.assertEquals(2,max);
    }
    @Test
    public void test_4() {
        int max = solution.largestRectangleArea(new int[]{1,2,1});
        Assert.assertEquals(3,max);
    }
    @Test
    public void test_5() {
        int max = solution.largestRectangleArea(new int[]{2,1,2});
        Assert.assertEquals(3,max);
    }
    @Test
    public void test_6() {
        int max = solution.largestRectangleArea(new int[]{1,3,2,3});
        Assert.assertEquals(6,max);
    }
    @Test
    public void test_7() {
        int max = solution.largestRectangleArea(new int[]{5,4,1,2});
        Assert.assertEquals(8,max);
    }
}

感情下次写算法的时候，能少写一个{绝不多写一个}，哈哈哈

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