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Letter Combinations of a Phone Number
mediumRecursion & Backtracking+20 XPTime limit 2s
On a phone keypad, each digit 2–9 maps to letters: 2 → abc, 3 → def, 4 → ghi, 5 → jkl, 6 → mno, 7 → pqrs, 8 → tuv, 9 → wxyz. Print every letter string the digits could represent.
Input: one line of digits (each 2–9).
Output: all combinations, one per line, in alphabetical order.
Constraints: 1 ≤ number of digits ≤ 6.
Think about it: one level of recursion per digit, one branch per letter. Trying letters in keypad order already gives alphabetical output.
Sample input 1
23
Sample output 1
ad ae af bd be bf cd ce cf
Sample input 2
2
Sample output 2
a b c
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Read input from standard input and print the answer to standard output. Your code runs in a secure sandbox against the samples (Run) and hidden tests (Submit).