leetcode--Maximal Rectangle

水深无声 2021-10-25 12:42 208阅读 0赞

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

public class Solution {
        public int maximalRectangle(char[][] matrix) {
            int row = matrix.length;
    		if(row == 0) return 0;
    		
    		int column = matrix[0].length;
    		int[][] consecutiveOnes = new int[row][column];
    		for(int i = 0; i < row; ++i) {
    			for(int j = 0; j < column; ++j){
    				if(matrix[i][j] - '0' == 1){
    					if(j == 0) 
    						consecutiveOnes[i][j] = 1;
    					else 
    						consecutiveOnes[i][j] = consecutiveOnes[i][j - 1] + 1;
    				}
    				else
    					consecutiveOnes[i][j] = 0;
    			}
    		}
    		
    		//calculate the max area. we check each element of consecutiveOnes column by column 
    		int maxArea = 0;
    		for(int i = 0; i < column; ++i){
    			for(int j = 0; j < row; ++j){
    				if(consecutiveOnes[j][i] != 0){
    					int minWidth = consecutiveOnes[j][i];
    					int index = j;
    					while(index >= 0 && consecutiveOnes[index][i] != 0){
    						minWidth = Math.min(minWidth, consecutiveOnes[index][i]);
    						maxArea = Math.max(maxArea, minWidth * (j - index + 1));
    						--index;
    					}
    				}
    			}
    		}
    		return maxArea;
        }
    }

Remark: the second part (to seek the max area) can be solved by method used in "largest rectangle histogram" problem. Therefore, there is an algorithm with time O(row \* column).

转载于:https://www.cnblogs.com/averillzheng/p/3825713.html