Replace a space in a string with%20

This substitution issue is to consider whether the original string will be overwritten if it is replaced directly on the source string.

Seeing this problem, I think a lot of people would think of replacing it directly from the beginning, that is, when you encounter a space, replace it with%20, and each time the character after the space is shifted by two bytes. The time complexity of this solution is O (n^2) ...

Another good solution is to replace from the back, the concrete way is to calculate all the space from the beginning of the calculation of the total length. The precondition of this solution is that if the source string is replaced, the source string will have enough space to accommodate the new string. Time Complexity of O (n) ...

void Replaceblank (char *string, int length) {if (string = = NULL | | length <= 0) {
    return;
    } int originallength = 0;
    int numberofblank = 0;
    int i = 0;
        while (string[i]! = ' + ') {originallength++;
        if (string[i] = = ") {numberofblank++;
    } ++i;
    } int newlength = Originallength + Numberofblank * 2;
    if (Newlength > Length) {return;
    } int indexoforiginal = Originallength;

    int indexofnew = Newlength; 
        while (indexoforiginal >= 0 && indexofnew > Indexoforiginal) {if (string[indexoforiginal] = = ")
            {string[indexofnew--] = ' 0 ';
            string[indexofnew--] = ' 2 ';
        string[indexofnew--] = '% ';
        } else {string[indexofnew--] = string[indexoforiginal];
    }--indexoforiginal; }
}