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Kth Smallest Number in M Sorted Lists

Explore how to find the kth smallest number across multiple sorted lists using a k-way merge technique. Understand problem constraints and implement solutions that handle duplicates and empty inputs effectively.

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Statement

Given a list, lists, containing mm sorted lists of integers in ascending order, and an integer k, find the kthk^{th} smallest element among all the lists.

Even if some values appear multiple times across the lists, each occurrence is treated as a unique element when determining the kthk^{th} smallest number.

If k exceeds the total number of elements across all lists, return the largest element among them. If the lists are empty, return 0.

Constraints:

  • 1≤m≤501\leq m \leq50
  • 0≤0\leq lists[i].length ≤50\leq 50
  • −109≤-10^9\leq lists[i][j] ≤109\leq 10^9
  • 1≤1\leq k ≤109\leq 10^9

Examples

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Understand the problem

Let’s take a moment to make sure you’ve correctly understood the problem. The quiz below helps you check if you’re solving the correct problem:

KthK^{th} Smallest Number in MM Sorted Lists

1.

What is the output if the following lists and the value of k are given as input?

list1 = [1, 4, 5]

list2 = [4, 7, 8]

list3 = [2, 6, 9]

k = 5

A.

7

B.

5

C.

6

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Figure it out!

We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Sequence - Vertical
Drag and drop the cards to rearrange them in the correct sequence.
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Try it yourself

Implement your solution in main.py in the following coding playground.

Python
usercode > main.py
from heapq import *





def k_smallest_number(lists, k):



    # Replace this placeholder return statement with your code

    

    return -1
Kth Smallest Number in M Sorted Lists