Solution to the Happy Ladybugs problems. https://www.hackerrank.com/challenges/happy-ladybugs

happy_ladybugs.py

#!/bin/python

import sys

def happy_ladybugs(n, bugs):
    mappings = {}
    free_cell = False
    happy = True
    
    for i, bug in enumerate(bugs):
        if i == 0 and i + 1 < len(bugs):
            happy = bug == bugs[i + 1]
        elif i == len(bugs) - 1:
            happy = bugs[i - 1] == bug and happy
        else:
            happy = happy and (bugs[i - 1] == bug or bugs[i + 1] == bug)
        
        # count the bugs
        if bug == '_':
            free_cell = True
        elif bug in mappings:
            mappings[bug] += 1
        else:
            mappings[bug] = 1
    
    singles = 0
    
    for bug, count in mappings.items():
        if count == 1:
            singles += 1
            
            
    if singles > 0:
        return 'NO'
    
    if not free_cell:
        return 'YES' if happy else 'NO'
    
    return 'YES'
            

games = int(raw_input())

for _ in xrange(games):
    n = int(raw_input())
    b = raw_input()
    
    print happy_ladybugs(n, b)

sample_input.txt

37
1
_
1
X
2
XX
2
X_
2
XY
3
X_X
3
XYX
3
XYZ
3
_XX
3
YXX
3
X__
3
X_Y
4
XXYY
4
XXYZ
4
XYXY
4
XXXY
4
XYXX
4
X_XX
4
X__X
4
XY_X
4
X___
5
XYZZZ
5
X_XYY
5
_XY_Y
5
_XX__
5
_XXYY
5
X_XYY
5
X___X
5
X__YX
6
X_X_Y_
6
XXXYYY
6
____ZZ
6
XYZYZY
6
XXYYZZ
6
X_XYXY
7
XZY_YZX
7
_XYYYXX

sample_output.txt

YES
NO
YES
NO
NO
YES
NO
NO
YES
NO
NO
NO
YES
NO
NO
NO
NO
YES
YES
NO
NO
NO
YES
NO
YES
YES
YES
YES
NO
NO
YES
YES
NO
YES
YES
YES
YES