[leetcode]85. Maximal Rectangle 最大矩形

Given a 2D binary matrix filled with 0's and 1's, find the largest rectangle containing only 1's and return its area.

Example:

Input:
[
  ["1","0","1","0","0"],
  ["1","0","1","1","1"],
  ["1","1","1","1","1"],
  ["1","0","0","1","0"]
]
Output: 6

 

题意

给定一个01矩阵，找出其中全由1构成的最大矩形。

 

思路

将所有1连接的部分看成一个bar height，这个题就可以看成是[leetcode]84. Largest Rectangle in Histogram直方图中的最大矩形

的followup，进行代码复用

 

代码

class Solution {
    public int maximalRectangle(char[][] matrix) {
       if(matrix.length==0 || matrix[0].length==0) return 0;
       int row = matrix.length;
        int col = matrix[0].length;
        int [] heights = new int[col];
        int area = 0;
        for(int i = 0; i< row; i++){
            for(int j = 0; j< col; j++){
                if(matrix[i][j]=='1'){
                    heights[j]++;
                }else{
                    heights[j]=0;
                }
                
            }     
           area = Math.max(area,  largestRectangle(heights));
        }
         return area;     
    }
    
    public int largestRectangle(int[] heights ){
        int area = 0;
        Stack<Integer> s = new Stack<>();
        for(int i = 0; i<=heights.length;){
            int value = i<heights.length ? heights[i] : 0;
            if(s.isEmpty() || value > heights[s.peek()]){
                s.push(i);
                i++;
            }else{
                int temp = s.pop();
                area = Math.max(area, heights[temp]*(s.isEmpty()? i: i-s.peek()-1));
            }// end else 
        }// end for 
        return area; 
    }
}