1738. Find Kth Largest XOR Coordinate Value

Problem Link

Description

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You are given a 2D matrix of size m x n, consisting of non-negative integers. You are also given an integer k.

The value of coordinate (a, b) of the matrix is the XOR of all matrix[i][j] where 0 <= i <= a < m and 0 <= j <= b < n (0-indexed).

Find the kth largest value (1-indexed) of all the coordinates of matrix.

 

Example 1:

Input: matrix = [[5,2],[1,6]], k = 1
Output: 7
Explanation: The value of coordinate (0,1) is 5 XOR 2 = 7, which is the largest value.

Example 2:

Input: matrix = [[5,2],[1,6]], k = 2
Output: 5
Explanation: The value of coordinate (0,0) is 5 = 5, which is the 2nd largest value.

Example 3:

Input: matrix = [[5,2],[1,6]], k = 3
Output: 4
Explanation: The value of coordinate (1,0) is 5 XOR 1 = 4, which is the 3rd largest value.

 

Constraints:

• m == matrix.length
• n == matrix[i].length
• 1 <= m, n <= 1000
• 0 <= matrix[i][j] <= 106
• 1 <= k <= m * n

Solution

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Python3

class Solution:
    def kthLargestValue(self, matrix: List[List[int]], k: int) -> int:
        rows, cols = len(matrix), len(matrix[0])
        res = []
        
        for i in range(rows):
            for j in range(cols):
                if i:
                    matrix[i][j] ^= matrix[i-1][j]
                if j:
                    matrix[i][j] ^= matrix[i][j-1]
                if i and j:
                    matrix[i][j] ^= matrix[i-1][j-1]
                
                res.append(matrix[i][j])
                
        return sorted(res)[-k]