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LeetCode17.java
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68 lines (50 loc) · 1.64 KB
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package LeetCode;
import java.util.ArrayList;
import java.util.List;
public class LeetCode17 {
/// 17. Letter Combinations of a Phone Number
/// https://leetcode.com/problems/letter-combinations-of-a-phone-number/description/
/// 时间复杂度: O(2^len(s))
/// 空间复杂度: O(len(s))
private String letterMap[] = {
" ", //0
"", //1
"abc", //2
"def", //3
"ghi", //4
"jkl", //5
"mno", //6
"pqrs", //7
"tuv", //8
"wxyz" //9
};
private ArrayList<String> res;
public List<String> letterCombinations(String digits) {
res = new ArrayList<>();
if (digits.equals(""))
return res;
findCombination(digits, 0, "");
return res;
}
// s中保存了此时从digits[0...index-1]翻译得到的一个字母字符串
// 寻找和digits[index]匹配的字母, 获得digits[0...index]翻译得到的解
private void findCombination(String digits, int index, String s) {
if (index == digits.length()) {
res.add(s);
return;
}
Character c = digits.charAt(index);
String letters = letterMap[c - '0'];
for (int i = 0; i < letters.length(); i++) {
findCombination(digits, index + 1, s + letters.charAt(i));
}
return;
}
private static void printList(List<String> list) {
for (String s : list)
System.out.println(s);
}
public static void main(String[] args) {
printList((new LeetCode17()).letterCombinations("234"));
}
}