[C language] [sword finger offer article] - replace spaces

Title Description

Please implement a function , Put the string s Replace each space in with "%20".

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source ： Power button （LeetCode）
link ：https://leetcode-cn.com/problems/ti-huan-kong-ge-lcof/
Copyright belongs to the network . For commercial reprint, please contact the official authority , Non-commercial reprint please indicate the source .

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ideas

  Using the double pointer idea , The first pointer traverses the array to find each space , And replace the space with ’\0’ , The second pointer points to the first address of the source string , And then use it strcat Move the address indicated by the second pointer to the first ’\0’ The string of is appended to the destination address , Last , The second pointer moves to the next address of the first pointer , loop , Until the source string is traversed .( The idea was inspired by the solution of a big man ： The most coquettish I'm here , are you ready )

Code implementation

char* replaceSpace(char* s){
    
    
    char *restr = NULL;
    char *str = "%20";
    int i = 0;
    char *ptr = s;
    int len = 0;

    len = strlen(s);

    restr = malloc(sizeof(char)*len*3+1);
    if(restr == NULL)
    {
    
        printf("malloc failed!\n");
        return NULL;
    }

    restr[0] = '\0';
    
    for(i = 0; s[i] != '\0'; i++)
    {
    
        if(s[i] != ' ')
        {
    
            continue;
        }

        s[i] = '\0';

        strcat(restr,ptr);
        strcat(restr,str);
        ptr = s + i + 1;
    }

    strcat(restr,ptr);

    return restr;
}

  When malloc And strcat When used in combination , One thing to note ：malloc The allocated memory will be automatically added to the end address \0,strcat Will appear first from the address \0 Start adding , So the sentence restr[0] = '\0'; Is the essence of the whole algorithm . At that time, there were always cross-border operations , Also depressed for a long time .