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LeetCode (力扣) 17. Letter Combinations of a Phon (C) - Medium (递归法)

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传统手机透过数字键来打字,一个数字键通常代表了多个英文字母,例如2 代表a , b , c ,3 代表d , e , f 等,连续按多个键能产生英文字母的组合,此题为给定数字,输出所有可能的英文字母组合。

题目与范例如下

這張圖片的 alt 屬性值為空,它的檔案名稱為 200px-Telephone-keypad2.svg.png

Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent. Return the answer in any order.

A mapping of digit to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters.

Example 1:

Input: digits = "23"
Output: ["ad","ae","af","bd","be","bf","cd","ce","cf"]
Example 2:

Input: digits = ""
Output: []
Example 3:

Input: digits = "2"
Output: ["a","b","c"]

Constraints:

0 <= digits.length <= 4
digits[i] is a digit in the range ['2', '9'].
Accepted
861,326
Submissions
1,706,491


 

解题方式为透过递归的方式,透过 for 回圈把每个数字可能的英文字母遍历出来,分别递归。填完字母后,补上结束字元 ' \0 ' 转存回要回传的空间内。

 

下方为我的代码

char map[10][5]={{},{},{'a','b','c'},{'d','e','f'},{'g','h','i'},{'j','k','l'},{'m','n','o'},{'p','q','r','s'},{'t','u','v'},{'w','x','y','z'}};
int reindex = 0;
char **re;
char *DPtr;
void Rnum( int index, char *tempstr){  // index use for input string index and tempstr index
	if(DPtr[index] == '\0'){
		tempstr[index] = '\0';
		re[reindex] = (char*)malloc(sizeof(char)*(strlen(DPtr)+1));
		strcpy(re[reindex],tempstr);
		reindex++;
	}
	else{
		for(int i = 0;i<strlen(map[DPtr[index]-'0']);i++){
			tempstr[index] = map[DPtr[index]-'0'][i];
			Rnum(index+1,tempstr);
		}
	}
}

char ** letterCombinations(char * digits, int* returnSize){
	DPtr = digits;
    reindex = 0;
	
    if(strlen(digits) != 0){
        (*returnSize) = 1;
        for(int i = 0 ; i < strlen(digits) ; i++ ){
            (*returnSize) *= strlen(map[digits[i]-'0']);
        }
    }
    else{
        (*returnSize) = 0;
    }
	re = (char**)malloc(sizeof(char*)*(*returnSize));
   
	char tempstr[5] = {0};
    if((*returnSize)>0)
	    Rnum( 0, tempstr);

    return re;

}

 

下方为时间与空间之消耗

Runtime: 0 ms, faster than 100 % of C online submissions for Letter Combinations of a Phone Number.

Memory Usage: 5.7 MB, less than 98.79 % of C online submissions for Letter Combinations of a Phone Number.

 

标签:digits,index,char,Medium,17,reindex,力扣,re,tempstr
来源: https://blog.csdn.net/JuzerTech/article/details/117983515