02-2. 一元多项式求导 (PAT)

#include <iostream>
#include <string>
#include <stdlib.h>
using namespace std;

typedef struct node{
    int coef;
    int expon;
    struct node *next;
} *PtrPolyNode, PolyNode;

PtrPolyNode createList();
void deriPoly( PtrPolyNode headNode );
void printPoly( PtrPolyNode headNode );

int main()
{
    PtrPolyNode headNode;
    headNode = createList();
    deriPoly( headNode );
    printPoly( headNode );
    return 0;
}

PtrPolyNode createList()
{
    PtrPolyNode headNode = NULL, currentNode = NULL, prevNode = NULL;
    do
    {
        currentNode = (PtrPolyNode)malloc( sizeof( PolyNode ) );
        cin >> currentNode->coef >> currentNode->expon;
        currentNode->next = NULL;
        if ( headNode == NULL )
        {
            headNode = currentNode;
            prevNode = currentNode;
            continue;
        }
        prevNode->next = currentNode;
        prevNode = currentNode;
    }
    while ( cin.get() != ‘\n‘ );
    return headNode;
}

void deriPoly( PtrPolyNode headNode )
{
    PtrPolyNode prev, cur;
    cur = prev = headNode;
    if ( headNode->next == NULL && headNode->expon == 0 )    //point
    {
        headNode->coef = 0;
        return;
    }
    while( cur != NULL )
    {
        if ( cur->expon == 0 )    //point
        {
            prev->next = NULL;
            free( cur );
            break;
        }
        cur->coef = cur->coef * cur->expon;
        cur->expon = cur->expon - 1;
        prev = cur;
        cur = cur->next;
    }
    return;
}

void printPoly( PtrPolyNode headNode )
{
    PtrPolyNode ptr;
    ptr = headNode;
    while ( ptr != NULL )
    {
        if ( ptr->next == NULL )
        {
            cout << ptr->coef << ‘ ‘ << ptr->expon; 
        }
        else
        {
            cout << ptr->coef << ‘ ‘ << ptr->expon << ‘ ‘;
        }
        ptr = ptr->next;
    }
    return;
}