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Letter Combinations of a Phone Number in Python
Suppose we have a string containing digits from 2-9 inclusive. We have to return all possible letter combinations that the number could represent. One mapping of digit to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters.
| 1 | 2 a b c | 3 d e f |
| 4 g h i | 5 j k l | 6 m n o |
| 7 p q r s | 8 t u v | 9 w x y z |
| * | 0 | # |
For an example, if the given string is “23”, then the possible strings will be [“ad”, “ae”, “af”, “bd”, “be”, “bf”, “cd”, “ce”, “cf”]
To solve this, we will follow these steps −
- Define an array called solve to solve the problem recursively
- solve method takes digits, characters, result, current_string and current_level, the function will be like
- if current_level = length of digits, then add current string after the result, and return
- for all characters i in characters[digits[current_level]]
- perform solve(digits, characters, result, current_string + i, current_level + 1)
- The actual function will be like
- if digits length is 0, then return an empty list
- define one map to hold numbers and corresponding characters as a string
- result := an empty list
- call solve(digits, characters, result, “”, 0)
Example(Python)
Let us see the following implementation to get a better understanding −
class Solution(object):
def letterCombinations(self, digits):
if len(digits) == 0:
return []
characters = {2:"abc",3:"def",4:"ghi",5:"jkl",6:"mno",7:"pqrs",8:"tuv",9:"wxyz"}
result = []
self.solve(digits,characters,result)
return result
def solve(self, digits, characters, result, current_string="",current_level = 0):
if current_level == len(digits):
result.append(current_string)
return
for i in characters[int(digits[current_level])]:
self.solve(digits,characters,result,current_string+i,current_level+1)
ob1 = Solution()
print(ob1.letterCombinations("37"))Input
"37"
Output
["dp","dq","dr","ds","ep","eq","er","es","fp","fq","fr","fs"]
Updated on: 27-Apr-2020
2K+ Views
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