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Letter Combinations of a Phone Number
Given a digit string, return all possible letter combinations that the number could represent.
A mapping of digit to letters (just like on the telephone buttons) is given below.
Input:Digit string "23"Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].Note:
Although the above answer is in lexicographical order, your answer could be in any order you want.
思路：使用BFS即可。
1 class Solution { 2 public: 3 vector<string> letterCombinations( string digits ) { 4 vector<string> combinations[2] = { vector<string>( 1, "" ) }; 5 for( size_t i = 0; i != digits.length(); ++i ) { 6 combinations[(i+1)%2].clear(); 7 for( auto iter = combinations[i%2].begin(); iter != combinations[i%2].end(); ++iter ) { 8 if( digits[i] >= ‘2‘ && digits[i] <= ‘8‘ && digits[i] != ‘7‘ ) { 9 for( int k = 0; k < 3; ++k ) {10 combinations[(i+1)%2].push_back( *iter );11 combinations[(i+1)%2].back().push_back( digits[i] != ‘8‘ ? 3*(digits[i]-‘2‘)+k+‘a‘ : k+‘t‘ );12 }13 } else if( digits[i] == ‘7‘ || digits[i] == ‘9‘ ) {14 for( int k = 0; k < 4; ++k ) {15 combinations[(i+1)%2].push_back( *iter );16 combinations[(i+1)%2].back().push_back( digits[i] == ‘7‘ ? k+‘p‘ : k+‘w‘ );17 }18 }19 }20 }21 return combinations[digits.length()%2];22 }23 };
Letter Combinations of a Phone Number
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