Python: Check if the letters of a given string can be rearranged so that two characters that are adjacent to each other are different

Python heap queue algorithm: Exercise-15 with Solution

Write a Python program to check if the letters of a given string can be rearranged so that two characters that are adjacent to each other are different using Heap queue algorithm.

Note:
If there is no output return the empty string.

Sample Solution:

Python Code:

import heapq
from collections import Counter
def reorganizeString(S):
    ctr = Counter(S)
    heap = [(-value, key) for key, value in ctr.items()]
    heapq.heapify(heap)
    if (-heap[0][0]) * 2 > len(S) + 1: 
        return ""
    ans = []
    while len(heap) >= 2:
        nct1, char1 = heapq.heappop(heap)
        nct2, char2 = heapq.heappop(heap)
        ans.extend([char1, char2])
        if nct1 + 1: heapq.heappush(heap, (nct1 + 1, char1))
        if nct2 + 1: heapq.heappush(heap, (nct2 + 1, char2))
    return "".join(ans) + (heap[0][1] if heap else "")

print(reorganizeString("aab"))
print(reorganizeString("abc"))
print(reorganizeString("aabb"))
print(reorganizeString("abccdd"))

Sample Output:

aba
abc
abab
cdabcd

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