题目解析

Example:
Input: “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 o

思路方法和代码演示:

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/**
* Created by dylan on 2018/3/22.
* 电话号码的组合
* 分析思路 比如输入123 实际是输入12的结果加上和3对应的组合
*/
public class A17PhoneCombine {
public List<String> letterCombinations(String digits) {
List<String> result = new ArrayList<String>(); //字母组合结果
if (digits == null || digits.length() == 0) {
return result;
}
Map<Character, String> dict = new HashMap<Character, String>(); // 初始化拨号T9键盘字典
dict.put('1', "");
dict.put('2', "abc");
dict.put('3', "def");
dict.put('4', "ghi");
dict.put('5', "jkl");
dict.put('6', "mno");
dict.put('7', "pqrs");
dict.put('8', "tuv");
dict.put('9', "wxyz");
dict.put('0', " ");
for (char tmp : digits.toCharArray()) {// 循环1
String val = dict.get(tmp);
if (val == null) {
return new ArrayList<String>();
}
List<String> tmpArray = new ArrayList<String>();
for (int i = 0; i < val.length(); i++) {//循环1 的结果result 和 当前tmp数字对应字母组合的处理逻辑
if (result.size() == 0) {
result.add("");
}
for (String item : result) {
tmpArray.add(item + val.charAt(i));
}
}
result = tmpArray; // 更新当前循环的结果数组
}
return result;
}
public static void main(String[] args) {
A17PhoneCombine a17PhoneCombine = new A17PhoneCombine();
System.out.println(a17PhoneCombine.letterCombinations("123"));
}
}

代码文件:
A17PhoneCombine.java

总结

  • 回溯上次处理结果,类似问题还有排列组合

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