Maximal Rectangle

ref

// http://www.cnblogs.com/springfor/p/3869492.html
// http://blog.csdn.net/linhuanmars/article/details/24444491

//https://leetcode.com/problems/largest-rectangle-in-histogram/

参考Largest Rectangle in Histogram(算法复杂度是O(n)

算法总时间复杂度是O(m*n)

public class Solution {
    public int maximalRectangle(char[][] matrix) {
        if(matrix==null|| matrix.length==0|| matrix[0].length==0) return 0;
        int m = matrix.length, n = matrix[0].length;
        int[] hl = new int[n];
        int res = 0;
        for(int i=0;i<m;i++){
            for(int j=0; j<n; j++){
                if(matrix[i][j]=='0'){
                    hl[j]=0;
                }else
                    hl[j]++;
            }
            res = Math.max(res, LargestRectangle(hl));
        }
        return res;
    }
    public int LargestRectangle(int[] his){
        int len =his.length+1;
        int[] h = new int[len];
        h = Arrays.copyOf(his, len);
        int res=0, i=0;
        Stack<Integer> st = new Stack<Integer>();
        while(i<len){
            if(st.isEmpty()||h[st.peek()]<=h[i]){
                st.push(i++);  // must increase i here! always forgot
            }else{
                int t = st.pop();
                res = Math.max(res, h[t]*(st.isEmpty()?i:i-st.peek()-1));
            }
        }
        return res;
    }
}