leetcode - 85.Maximal Rectangle

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 0
1 0 1 1 1
1 1 1 1 1
1 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;
  }