AoC-2022 Day 13a -- single pass no allocations

#include <stdio.h>

char input[] = R"([1,1,3,1,1]
[1,1,5,1,1]

[[1],[2,3,4]]
[[1],4]

[9]
[[8,7,6]]

[[4,4],4,4]
[[4,4],4,4,4]

[7,7,7,7]
[7,7,7]

[]
[3]

[[[]]]
[[]]

[1,[2,[3,[4,[5,6,7]]]],8,9]
[1,[2,[3,[4,[5,6,0]]]],8,9]
)";

/*
*
* LEFT := LIST
* RIGHT := LIST
* LIST := '[' (BODY)? ']'
* BODY := ELEM (',' ELEM)*
* ELEM := NUM | LIST
*
* TODO: s/int&/int*/
*/

int myParseCompareElem(const char* strL, int& posL, const char* strR, int& posR, int& order);
int myParseCompareBody(const char* strL, int& posL, const char* strR, int& posR, int& order);
int myParseCompareList(const char* strL, int& posL, const char* strR, int& posR, int& order);


int myParseCompareElem(const char* strL, int& posL, const char* strR, int& posR, int& order)
{
    int res = 0;
    char cl = strL[posL];
    char cr = strR[posR];

    if (('[' != cl) && (cl < '0' || cl > '9'))
        return posL;    // error
    if (('[' != cr) && (cr < '0' || cr > '9'))
        return posR;    // error

    bool isListL = ('[' == cl);
    bool isListR = ('[' == cr);

    int vall = 0;
    int valr = 0;
    if (!isListL)
    {
        while (cl >= '0' && cl <= '9')
        {
            vall += vall * 10 + cl - '0';
            posL++;
            cl = strL[posL];
        }
    }

    if (!isListR)
    {
        while (cr >= '0' && cr <= '9')
        {
            valr += valr * 10 + cr - '0';
            posR++;
            cr = strR[posR];
        }
    }

    if (isListL && !isListR)
    {
        char buf[40];
        sprintf_s(buf, "[%d]", valr);
        int tempPos = 0;
        res = myParseCompareList(strL, posL, buf, tempPos, order);
        if (res)
            return res;    // error
        if (order)
            return 0;
    }
    else if (!isListL && isListR)
    {
        char buf[40];
        sprintf_s(buf, "[%d]", vall);
        int tempPos = 0;
        res = myParseCompareList(buf, tempPos, strR, posR, order);
        if (res)
            return res;    // error
        if (order)
            return 0;
    }
    else if (isListL && isListR)
    {
        res = myParseCompareList(strL, posL, strR, posR, order);
        if (res)
            return res;    // error
        if (order)
            return 0;
    }
    else if (!isListL && !isListR)
    {
        order = valr - vall;
    }

    return 0;
}

int myParseCompareBody(const char* strL, int& posL, const char* strR, int& posR, int& order)
{
    int res = 0;
    res = myParseCompareElem(strL, posL, strR, posR, order);
    if (res)
        return res;    // error
    if (order)
        return 0;

    int contL = (',' == strL[posL]);
    int contR = (',' == strR[posR]);

    order = contR - contL;
    if (order)
        return 0;

    while (contL && contR)
    {
        posL++;
        posR++;

        res = myParseCompareElem(strL, posL, strR, posR, order);
        if (res)
            return res;    // error
        if (order)
            return 0;

        int contL = (',' == strL[posL]);
        int contR = (',' == strR[posR]);

        order = contR - contL;
        if (order)
            return 0;
    }

    return 0;
}

int myParseCompareList(const char* strL, int & posL, const char* strR, int& posR, int & order)
{
    int res = 0;
    if ('[' != strL[posL])
        return posL;    // error
    if ('[' != strR[posR])
        return posR;    // error
    posL++;
    posR++;

    int bodyPresentL = (']' != strL[posL]);
    int bodyPresentR = (']' != strR[posR]);

    order = bodyPresentR - bodyPresentL;
    if (order)
        return 0;

    if (bodyPresentL && bodyPresentR)
    {
        res = myParseCompareBody(strL, posL, strR, posR, order);
        if (res)
            return res;    // error
        if (order)
            return 0;
    }

    posL++;
    posR++;

    return 0;
}


int main()
{
    int i = 0;
    int pos = 0;
    int index = 0;
    int score = 0;

    int beginL = 0;
    int beginR = 0;

    while (input[i])
    {
        char c = input[i++];

        if ('\n' == c)
        {
            pos++;
            pos %= 3;
            if (0 == pos)
                beginL = i;
            if (1 == pos)
                beginR = i;
            if (2 == pos)
            {
                int order = 0;

                int err = myParseCompareList(input, beginL, input, beginR, order);

                index++;
                if (order >= 0)
                    score += index;
            }
            continue;
        }
    }

    printf("%d\n", score);
}