93 lines
2.6 KiB
Java
93 lines
2.6 KiB
Java
//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。答案可以按 任意顺序 返回。
|
||
//
|
||
// 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 1：
|
||
//
|
||
//
|
||
//输入：digits = "23"
|
||
//输出：["ad","ae","af","bd","be","bf","cd","ce","cf"]
|
||
//
|
||
//
|
||
// 示例 2：
|
||
//
|
||
//
|
||
//输入：digits = ""
|
||
//输出：[]
|
||
//
|
||
//
|
||
// 示例 3：
|
||
//
|
||
//
|
||
//输入：digits = "2"
|
||
//输出：["a","b","c"]
|
||
//
|
||
//
|
||
//
|
||
//
|
||
// 提示：
|
||
//
|
||
//
|
||
// 0 <= digits.length <= 4
|
||
// digits[i] 是范围 ['2', '9'] 的一个数字。
|
||
//
|
||
// Related Topics 哈希表 字符串 回溯 👍 1453 👎 0
|
||
|
||
package leetcode.editor.cn;
|
||
|
||
import java.util.ArrayList;
|
||
import java.util.HashMap;
|
||
import java.util.List;
|
||
import java.util.Map;
|
||
|
||
//17:电话号码的字母组合
|
||
class LetterCombinationsOfAPhoneNumber {
|
||
public static void main(String[] args) {
|
||
//测试代码
|
||
Solution solution = new LetterCombinationsOfAPhoneNumber().new Solution();
|
||
}
|
||
|
||
//力扣代码
|
||
//leetcode submit region begin(Prohibit modification and deletion)
|
||
class Solution {
|
||
public List<String> letterCombinations(String digits) {
|
||
List<String> combinations = new ArrayList<>();
|
||
if (digits.length() == 0) {
|
||
return combinations;
|
||
}
|
||
Map<Character, String> phoneMap = new HashMap<Character, String>() {{
|
||
put('2', "abc");
|
||
put('3', "def");
|
||
put('4', "ghi");
|
||
put('5', "jkl");
|
||
put('6', "mno");
|
||
put('7', "pqrs");
|
||
put('8', "tuv");
|
||
put('9', "wxyz");
|
||
}};
|
||
backtrack(combinations, phoneMap, digits, 0, new StringBuffer());
|
||
return combinations;
|
||
}
|
||
|
||
public void backtrack(List<String> combinations, Map<Character, String> phoneMap, String digits, int index, StringBuffer combination) {
|
||
if (index == digits.length()) {
|
||
combinations.add(combination.toString());
|
||
} else {
|
||
char digit = digits.charAt(index);
|
||
String letters = phoneMap.get(digit);
|
||
int lettersCount = letters.length();
|
||
for (int i = 0; i < lettersCount; i++) {
|
||
combination.append(letters.charAt(i));
|
||
backtrack(combinations, phoneMap, digits, index + 1, combination);
|
||
combination.deleteCharAt(index);
|
||
}
|
||
}
|
||
}
|
||
}
|
||
//leetcode submit region end(Prohibit modification and deletion)
|
||
|
||
} |