LeetCode 2388: Change Null Values in a Table to the Previous Value Solution

Master LeetCode problem 2388 (Change Null Values in a Table to the Previous Value), a medium challenge, with our optimized solutions in Java, C++, and Python. Explore detailed explanations, test your code in our interactive editor, and prepare for coding interviews.

2388. Change Null Values in a Table to the Previous Value

Medium

Database

Problem Explanation

Explanation:

Given a table with null values, the task is to change those null values to the value from the previous non-null cell in the same column.

Algorithm:

Iterate through each row of the table.
For each cell, if it is null, update it with the value of the previous non-null cell in the same column.
Keep track of the previous non-null value for each column.

Time Complexity: O(m*n) where m is the number of rows and n is the number of columns in the table. Space Complexity: O(n) where n is the number of columns in the table.

Solution Code

class Solution {
    public void fillTable(int[][] table) {
        if (table == null || table.length == 0) {
            return;
        }

        int numRows = table.length;
        int numCols = table[0].length;

        int[] prevValues = new int[numCols];
        Arrays.fill(prevValues, -1);

        for (int i = 0; i < numRows; i++) {
            for (int j = 0; j < numCols; j++) {
                if (table[i][j] == -1) {
                    table[i][j] = prevValues[j];
                } else {
                    prevValues[j] = table[i][j];
                }
            }
        }
    }
}

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