Grokking the Coding Interview: Patterns for Coding Questions

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Problem Challenge 1: Rearrange String K Distance Apart (hard)

Problem Statement

Given a string and a number ‘K’, find if the string can be rearranged such that the same characters are at least ‘K’ distance apart from each other.

Example 1:

Input: "mmpp", K=2
Output: "mpmp" or "pmpm"
Explanation: All same characters are 2 distance apart.

Example 2:

Input: "Programming", K=3
Output: "rgmPrgmiano" or "gmringmrPoa" or "gmrPagimnor" and a few more  
Explanation: All same characters are 3 distance apart.

Example 3:

Input: "aab", K=2
Output: "aba"
Explanation: All same characters are 2 distance apart.

Example 4: ``

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Shashwat Kumar

Shashwat Kumar

· 2 years ago

  • str consists of only lowercase English letters. - This is not correct as there are uppercase letters also.
P

Pete Stenger

· 2 years ago

from heapq import *
from collections import deque, Counter

class Solution:
  def reorganizeString(self, str, k):
    counts = Counter(str)
    heap = [
      (-value, char) for char, value in counts.items()
    ]
    heapify(heap)

    if -heap[0][0] > (len(str) + k - 1)//k:
      return ''
    
    res = list('_' * len(str))
    i = 0
    offset = 0
    while heap:
      count, char = heappop(heap)
      while count < 0:
        res[i] = char
        i += k
        if i >= len(res):
          offset += 1
          i = offset
        count += 1
    return ''.join(res)