17. Letter Combinations of a Phone Number
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Given a string containing digits from 2-9
inclusive, 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. Note that 1 does not map to any letters.
Example:
Input: "23" Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].
public class Solution public List<String> letterCombinations(String digits) //存放答案的list List<String> list=new ArrayList<String>(); //建立map存放手机按键 Map<String, String> map=new HashMap<String, String>(); map.put("2", "abc"); map.put("3", "def"); map.put("4", "ghi"); map.put("5", "jkl"); map.put("6", "mno"); map.put("7", "pqrs"); map.put("8", "tuv"); map.put("9", "wxyz"); //循环判断 for (int i = 0; i < digits.length(); i++) String s=digits.substring(i,i+1); //如果能查到数字键盘 //if (map.get(s)!=null) //如果list不为空,即并非刚开始 if (list.size()!=0) //记住目前list的长度 int size=list.size(); //循环list当前长度 for (int j = 0; j < size; j++) //将list中的每个值与接下来的对应数字键盘的可能性进行拼接 for (int k = 0; k <map.get(s).length(); k++) String a=list.get(j)+map.get(s).charAt(k); list.add(a); //删掉之前的list for (int j = size-1; j >=0; j--) list.remove(j); else for (int j = 0; j < map.get(s).length(); j++) String a=map.get(s).charAt(j)+""; list.add(a); // return list;
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