17. Letter Combinations of a Phone Number

本文介绍了一种使用Java实现的算法,该算法可以根据输入的数字字符串生成所有可能的字母组合,这些字母组合对应电话按键上的字母。通过递归地添加每个数字对应的字母到当前组合中,最终得到所有可能的组合。

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class Solution {
    public List<String> letterCombinations(String digits) {
       LinkedList<String> ans = new LinkedList<String>();
        String[] mapping = new String[] {"0", "1", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz"};
        if (digits.contains("1")||digits.contains("0")||"".equals(digits))return ans;
        ans.add("");
        for(int i =0; i<digits.length();i++){
            int x = Character.getNumericValue(digits.charAt(i));
            while(ans.peek().length()==i){
                String t = ans.remove();
                for(char s : mapping[x].toCharArray())
                    ans.add(t+s);
            }
        }
            return ans;
        }
}
(Telephone Number Word Generator) Standard telephone keypads contain the digits 0 through 9. The numbers 2 through 9 each have three letters associated with them, as is indicated by the following table: Many people find it difficult to memorize phone numbers, so they use the correspondence between digits and letters to develop seven-letter words that correspond to their phone numbers. For example, a person whose telephone number is 686-2377 might use the correspondence indi- cated in the above table to develop the seven-letter word “NUMBERS.” Businesses frequently attempt to get telephone numbers that are easy for their clients to remember. If a business can advertise a simple word for its customers to dial, then no doubt the business will receive a few more calls. Each seven-letter word corresponds to exactly one seven-digit telephone number. The restaurant wishing to increase its take-home business could surely do so with the number 825-3688 (i.e., “TAKEOUT”). Each seven-digit phone number corresponds to many separate seven-letter words. Unfortunately, most of these represent unrecognizable juxtaposi- tions of letters. It’s possible, however, that the owner of a barber shop would be pleased to know that the shop’s telephone number, 424-7288, corresponds to “HAIRCUT.” A veterinarian with the phone number 738-2273 would be happy to know that the number corresponds to “PETCARE.” Write a program that, given a seven-digit number, writes to a file every possible seven-letter word corresponding to that number. There are 2187 (3 to the seventh power) such words. Avoid phone numbers with the digits 0 and 1.
06-09
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