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String17.java
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62 lines (60 loc) · 1.95 KB
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package string;
import java.util.*;
/**
* @ProjectName: leetcode
* @Package: string
* @ClassName: String17
* @Author: markey
* @Description:17. 电话号码的字母组合
* 给定一个仅包含数字 2-9 的字符串，返回所有它能表示的字母组合。
*
* 给出数字到字母的映射如下（与电话按键相同）。注意 1 不对应任何字母。
*
*
*
* 示例:
*
* 输入："23"
* 输出：["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].
*
* 来源：力扣（LeetCode）
* 链接：https://leetcode-cn.com/problems/letter-combinations-of-a-phone-number
* 著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。
* @Date: 2020/5/2 0:47
* @Version: 1.0
*/
public class String17 {
private static Map<Character, char[]> map;
static {
map = new HashMap<>();
map.put('2', new char[] {'a', 'b', 'c'});
map.put('3', new char[] {'d', 'e', 'f'});
map.put('4', new char[] {'g', 'h', 'i'});
map.put('5', new char[] {'j', 'k', 'l'});
map.put('6', new char[] {'m', 'n', 'o'});
map.put('7', new char[] {'p', 'q', 'r', 's'});
map.put('8', new char[] {'t', 'u', 'v'});
map.put('9', new char[] {'w', 'x', 'y', 'z'});
}
public List<String> letterCombinations(String digits) {
List<String> res = new ArrayList<>();
if (digits.isEmpty()) {
return res;
}
if (digits.length() == 1) {
char[] chars = map.get(digits.charAt(0));
for (int i = 0; i < chars.length; i++) {
res.add(String.valueOf(chars[i]));
}
return res;
}
List<String> temp = letterCombinations(digits.substring(1));
temp.forEach(s -> {
char[] chars = map.get(digits.charAt(0));
for (int i = 0; i < chars.length; i++) {
res.add(chars[i] + s);
};
});
return res;
}
}