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

Last update on July 28 2025 13:06:55 (UTC/GMT +8 hours)

15. Rearrange String (No Adjacent Duplicates)

Write a Python program to check if the letters in a given string can be rearranged. This is to make sure that two characters that are adjacent to each other are different using the 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

Flowchart:

For more Practice: Solve these Related Problems:

• Write a Python program to determine if the letters of a string can be rearranged so that no two identical letters are adjacent using a max-heap.
• Write a Python script to rearrange a string using heapq so that identical characters are separated, and then print the rearranged string.
• Write a Python function to check if a valid rearrangement exists for a string using a heap-based algorithm and return a boolean value.
• Write a Python program to use a heap to rearrange characters in a string such that no two adjacent characters are the same, handling cases with high frequency letters.

Go to:

• Python Heap Queue Algorithm Exercises Home ↩
• Python Exercises Home ↩

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Next: Write a Python program which add integer numbers from the data stream to a heapq and compute the median of all elements.

Python Code Editor:

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