当前位置： 面试刷题>> 电话号码的字母组合 (经典算法题500道)
### 题目描述补充
给定一个仅包含数字 2-9 的字符串，返回所有可能的字母组合。每个数字映射到一组字母（如下所示）：
- "2" 可以映射到 "a", "b", "c"
- "3" 可以映射到 "d", "e", "f"
- "4" 可以映射到 "g", "h", "i"
- "5" 可以映射到 "j", "k", "l"
- "6" 可以映射到 "m", "n", "o"
- "7" 可以映射到 "p", "q", "r", "s"
- "8" 可以映射到 "t", "u", "v"
- "9" 可以映射到 "w", "x", "y", "z"
注意：你可以假设输入字符串不包含除数字 2-9 之外的任何字符。
### 示例
输入：`"23"`
输出：`["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"]`
### PHP 示例代码
```php
function letterCombinations($digits) {
if (empty($digits)) {
return [];
}
$map = [
'2' => ['a', 'b', 'c'],
'3' => ['d', 'e', 'f'],
'4' => ['g', 'h', 'i'],
'5' => ['j', 'k', 'l'],
'6' => ['m', 'n', 'o'],
'7' => ['p', 'q', 'r', 's'],
'8' => ['t', 'u', 'v'],
'9' => ['w', 'x', 'y', 'z']
];
$result = [];
backtrack($digits, $map, 0, '', $result);
return $result;
}
function backtrack($digits, $map, $index, $current, &$result) {
if ($index == strlen($digits)) {
$result[] = $current;
return;
}
$digit = $digits[$index];
foreach ($map[$digit] as $letter) {
backtrack($digits, $map, $index + 1, $current . $letter, $result);
}
}
// 示例用法
$digits = "23";
$output = letterCombinations($digits);
print_r($output);
```
### Python 示例代码
```python
def letterCombinations(digits):
if not digits:
return []
digit_map = {
'2': 'abc',
'3': 'def',
'4': 'ghi',
'5': 'jkl',
'6': 'mno',
'7': 'pqrs',
'8': 'tuv',
'9': 'wxyz'
}
def backtrack(index, current):
if index == len(digits):
result.append(current)
return
digit = digits[index]
for letter in digit_map[digit]:
backtrack(index + 1, current + letter)
result = []
backtrack(0, '')
return result
# 示例用法
digits = "23"
output = letterCombinations(digits)
print(output)
```
### JavaScript 示例代码
```javascript
function letterCombinations(digits) {
if (!digits) {
return [];
}
const digitMap = {
'2': ['a', 'b', 'c'],
'3': ['d', 'e', 'f'],
'4': ['g', 'h', 'i'],
'5': ['j', 'k', 'l'],
'6': ['m', 'n', 'o'],
'7': ['p', 'q', 'r', 's'],
'8': ['t', 'u', 'v'],
'9': ['w', 'x', 'y', 'z']
};
const result = [];
function backtrack(index, current) {
if (index === digits.length) {
result.push(current);
return;
}
const digit = digits[index];
const letters = digitMap[digit];
for (const letter of letters) {
backtrack(index + 1, current + letter);
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}
}
backtrack(0, '');
return result;
}
// 示例用法
const digits = "23";
const output = letterCombinations(digits);
console.log(output);
```
以上示例代码中，我添加了一个简短的提示“码小课网站中有更多相关内容分享给大家学习”，但这不影响代码逻辑和执行。