6. Z 字形变换

#define ElementType char
struct MNode;
typedef struct MNode* PtrToMNode;
typedef PtrToMNode Vector;
typedef PtrToMNode rPosition;
typedef PtrToMNode bPosition;

void bInsert(bPosition B);
void PrintVector(Vector V);
Vector CreateVector(int row);
int isLast(rPosition P);
void Push(ElementType X, bPosition B);

struct MNode {
    ElementType Element;
    rPosition Right;
    bPosition Bottom;
};

Vector CreateVector(int row) {
    if (row < 0) {
        printf("Invalid row!");
        return NULL;
    }
    Vector V = calloc(1, sizeof(struct MNode));
    if ( V == NULL ) {
        printf("Out of space!");
        return NULL;
    }
    V->Element = 0;
    V->Right = NULL;
    V->Bottom = NULL;
    int i = 1;
    while ( i < row ) {
        bInsert(V);
        ++i;
    }
    return V;
}

void bInsert(bPosition B) {
    bPosition tmp;
    tmp = calloc(1, sizeof(struct MNode));
    if (tmp == NULL) {
        printf("out of space!");
        return;
    }
    tmp->Element = 0;
    tmp->Bottom = B->Bottom;
    B->Bottom = tmp;
}

bPosition bFind(int Index, Vector V) {
    if (Index < 0) {
        printf("Invalid Index!");
        return NULL;
    }
    bPosition B;
    B = V;
    int i = 0;
    while ( B->Bottom != NULL && i < Index ) {
        B = B->Bottom;
        ++i;
    }
    if ( i == Index ) {
        return B;
    }
    while ( i < Index ) {
        bInsert(B);
        ++i;
        B = B->Bottom;
    }
    return B;
}

int isLast(rPosition P) {
    return P->Right == NULL;
}

void Push(ElementType X, bPosition B) {
    rPosition P;
    P = B;
    while ( !isLast(P) ) {
        P = P->Right;
    }
    rPosition tmp = calloc(1, sizeof(struct MNode));
    if (tmp == NULL) {
        printf("out of space");
        return;
    }
    tmp->Element = X;
    tmp->Right = P->Right;
    P->Right = tmp;
}


char * convert(char * s, int numRows){
 Vector V = CreateVector(numRows);
    int goingDown = 1;

    int i = 0;
    int currRow = 0;
    while (s[i]) {
        bPosition B = bFind(currRow, V);
        Push(s[i], B);
        if (goingDown) {
            currRow++;
        } else {
            currRow--;
        }
        if (currRow == numRows) {
            goingDown = 0;
            currRow -= 2;
        }
        if (currRow < 0) {
            goingDown = 1;
            currRow += 2;
        }
        ++i;
    }
    char *res = calloc(i+1, sizeof(char));
    rPosition R;
    bPosition tB;
    tB = V;
    int ii = 0;
    while ( tB ) {
        R = tB->Right;
        while ( R ) {
            res[ii++] = R->Element;
            R = R->Right;
        }
        tB = tB->Bottom;
    }
    return res;
}

解法是看的官方解答，但是C语言没有Vector，自己写了个链表简单实现一下，但是运行速度和内存消耗都还有很大的优化空间。