Leetcode 764. Largest Plus Sign

Gary Chiang
2 min readSep 9, 2021



You are given an integer n. You have an n x n binary grid grid with all values initially 1's except for some indices given in the array mines. The ith element of the array mines is defined as mines[i] = [xi, yi] where grid[xi][yi] == 0.

Return the order of the largest axis-aligned plus sign of 1’s contained in grid. If there is none, return 0.

An axis-aligned plus sign of 1's of order k has some center grid[r][c] == 1 along with four arms of length k - 1 going up, down, left, and right, and made of 1's. Note that there could be 0's or 1's beyond the arms of the plus sign, only the relevant area of the plus sign is checked for 1's.

Example 1:

Input: n = 5, mines = [[4,2]]
Output: 2
Explanation: In the above grid, the largest plus sign can only be of order 2. One of them is shown.

Example 2:

Input: n = 1, mines = [[0,0]]
Output: 0
Explanation: There is no plus sign, so return 0.


  • 1 <= n <= 500
  • 1 <= mines.length <= 5000
  • 0 <= xi, yi < n
  • All the pairs (xi, yi) are unique.


  1. find the largest PLUS sign, return the length from plus heart to plus arm
  2. create a new matrix, and fill all of them into 1, change mines to 0
  3. loop through the matrix, and if we see 0, change the matrix[i][j] into 0
  4. catch the max result at the end of the loop



Gary Chiang

CS new grad, 6 years experience related to supply chain management. Located in Bay area