leetcode 221: Maximal Square
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Maximal Square
Total Accepted: 1312 Total Submissions: 6388Given 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.
[思路]
dynamic programing. 以当前点(x,y) = ‘1‘ 为右下角的最大正方形的边长f(x,y) = min( f(x-1,y), f(x,y-1), f(x-1,y-1)) + 1.
递推公式已建立, dp就自然而然了.
[CODE]
public class Solution { public int maximalSquare(char[][] matrix) { if(matrix==null || matrix.length==0 || matrix[0].length==0) return 0; int n = matrix.length; int m = matrix[0].length; int[][] d = new int[n][m]; int max = 0; for(int i=0; i<n; i++) { if(matrix[i][0]=='1') { d[i][0] = 1; max = 1; } } for(int j=0; j<m; j++) { if(matrix[0][j]=='1') { d[0][j] = 1; max = 1; } } for(int i=1; i<n; i++) { for(int j=1; j<m; j++) { if(matrix[i][j]=='0') d[i][j]=0; else { d[i][j] = Math.min( Math.min( d[i-1][j], d[i][j-1]), d[i-1][j-1] ) + 1; max = Math.max(max, d[i][j]); } } } return max*max; } }
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