leetcode

Maximal Rectangle

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

For example, given the following matrix:

1 0 1 0 01 0 1 1 11 1 1 1 11 0 0 1 0

Return 6.

Solution:

  public int maximalRectangle(char[][] matrix) {    if (matrix == null || matrix.length == 0) {      return 0;    }    int m = matrix.length;    int n = matrix[0].length;    int[] left = new int[n];    int[] right = new int[n];    Arrays.fill(right, n);    int[] height = new int[n];    int maxArea = 0;    for (int i = 0; i < m; i++) {      int cur_left = 0;      int cur_right = n;      for (int j = 0; j < n; j++) {        if (matrix[i][j] == '1')          left[j] = Math.max(left[j], cur_left);        else {          left[j] = 0;          cur_left = j + 1;        }      }      for (int j = n - 1; j > -1; j--) {        if (matrix[i][j] == '1')          right[j] = Math.min(right[j], cur_right);        else {          right[j] = n;          cur_right = j;        }      }      for (int j = 0; j < n; j++) {        if (matrix[i][j] == '1')          height[j]++;        else          height[j] = 0;      }      for (int j = 0; j < n; j++) {        maxArea = Math.max(maxArea, height[j] * (right[j] - left[j]));      }    }    return maxArea;  }