17. Letter Combinations of a Phone Number (backtracking)

最新推荐文章于 2025-05-25 20:50:12 发布

转载最新推荐文章于 2025-05-25 20:50:12 发布 · 63 阅读

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原文链接：http://www.cnblogs.com/qionglouyuyu/p/5398527.html

本文介绍了一种基于递归回溯算法实现的电话号码字母组合生成方法。输入为一串数字，输出所有可能的字母组合。文章提供了详细的C语言代码实现，并通过一个具体的例子展示了如何根据电话按键上的数字映射到对应的字母。

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Given a digit string, return all possible letter combinations that the number could represent.

A mapping of digit to letters (just like on the telephone buttons) is given below.

Input:Digit string "23"
Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].

/**
 * Return an array of size *returnSize.
 * Note: The returned array must be malloced, assume caller calls free().
 */
char* digit2Letter(char digit){
    switch(digit){
    case '2':
      return "abc";
    case '3':
      return "def";
    case '4':
      return "ghi";
    case '5':
      return "jkl";
    case '6':
      return "mno";
    case '7':
      return "pqrs";
    case '8':
      return "tuv";
    case '9':
      return "wxyz";
    default:
      return "";
    }
}
 
char** letterCombinations(char* digits, int* returnSize) {
    char** returnArray = NULL;
    if(*digits == '\0') return returnArray;
    
    char* returnElem = malloc(sizeof(char)*sizeof(strlen(digits)));
    returnArray = malloc(sizeof(char*)*1000); 
    backTracking(digits, returnArray, returnSize, returnElem, 0);

    return returnArray;
}

void backTracking(char* digits, char** returnArray, int* returnSize, char* returnElem, int pElem){
    if(*digits == '\0'){
        (*returnSize)++;
        char* elem = malloc(sizeof(char)*pElem);
        memcpy(elem, returnElem, sizeof(char)*pElem);
        elem[pElem] = '\0';
        printf("elem[0] = %d, elem[1] = %d\n",elem[0],elem[1]);
        returnArray[*returnSize-1] = elem;
        return;
    }
    
    char* str = digit2Letter(*digits);
    int len = strlen(str);
    for(int i = 0; i < len; i++){
        returnElem[pElem] = str[i];

        backTracking(digits+1, returnArray, returnSize, returnElem, pElem+1 );
    }
}

转载于:https://www.cnblogs.com/qionglouyuyu/p/5398527.html