LeetCode Maximal Rectangle

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

题意：求0,1矩阵中，1构成的最大矩阵。

思路：借用了上一题，首先我们先计算出dp[i][j]表示到第i行第j列时，此时这一列的连续1的个数，然后计算每一行的时候，每一列都相当于一个直方图。

public class Solution {
     public int maximalRectangle(char[][] matrix) {
    	int n = matrix.length;
    	if (n == 0) return 0;
    	int m = matrix[0].length;
    	if (m == 0) return 0;
    	
    	int dp[][] = new int[n+1][m+1];
    	for (int i = 0; i < m; i++) 
    		if (matrix[0][i] == '1') 
    			dp[0][i] = 1;
    	
    	for (int j = 0; j < m; j++)
    		for (int i = 1; i < n; i++)
    			if (matrix[i][j] == '1') 
    				dp[i][j] = dp[i-1][j] + 1;
    	
    	int ans = 0;
    	for (int i = 0; i < n; i++) {
    		int tmp = largestRectangleArea(dp[i]);
    		ans = Math.max(ans, tmp);
    	}
    	
    	return ans;
    }
    
    public int largestRectangleArea(int[] height) {  
        Stack<Integer> stack = new Stack<Integer>();  
        int i = 0;  
        int ans = 0;  
        int h[] = new int[height.length+1];  
        h = Arrays.copyOf(height, height.length+1);  
        while (i < h.length) {  
            if (stack.isEmpty() || h[stack.peek()] <= h[i])  
                stack.push(i++);  
            else {  
                int t = stack.pop();  
                ans = Math.max(ans, h[t] * (stack.isEmpty() ? i : i - stack.peek() - 1));  
            }  
        }  
          
        return ans;  
    }  
}

LeetCode Maximal Rectangle

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原文地址：http://blog.csdn.net/u011345136/article/details/45008099