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Given a 2D binary matrix filled with 0‘s and 1‘s, find the largest square containing all 1‘s and return its area.
For example, given the following matrix:
1 0 1 0 0 1 0 1 1 1 1 1 1 1 1 1 0 0 1 0
Return 4.
题解来自 http://www.geeksforgeeks.org/maximum-size-sub-matrix-with-all-1s-in-a-binary-matrix/
反正我觉得是好聪明，俺想不出来
1) Construct a sum matrix S[R][C] for the given M[R][C].
a) Copy first row and first columns as it is from M[][] to S[][]
b) For other entries, use following expressions to construct S[][]
If M[i][j] is 1 then
S[i][j] = min(S[i][j-1], S[i-1][j], S[i-1][j-1]) + 1
Else /*If M[i][j] is 0*/
S[i][j] = 0
2) Find the maximum entry in S[R][C]
3) Using the value and coordinates of maximum entry in S[i], print
sub-matrix of M[][]
public class Solution { public int maximalSquare(char[][] matrix) { if(matrix==null||matrix.length==0||matrix[0].length==0) return 0; int m = matrix.length; int n = matrix[0].length; int[][] s = new int[m][n]; for(int i=0;i<m;i++){ if(matrix[i][0]==‘1‘) s[i][0]=1; } for(int j=1;j<n;j++){ if(matrix[0][j]==‘1‘) s[0][j]=1; } for(int i=1;i<m;i++){ for(int j=1;j<n;j++){ if(matrix[i][j]==‘1‘){ s[i][j] = Math.min(Math.min(s[i-1][j-1],s[i][j-1]),s[i-1][j])+1; }else s[i][j] = 0; } } int res =s[0][0]; for(int i=0;i<m;i++){ for(int j=0;j<n;j++){ res = Math.max(res,s[i][j]); } } return res*res ; } }
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原文地址：http://www.cnblogs.com/jiajiaxingxing/p/4553612.html
