【发布时间】：2014-09-25 22:18:06
【问题描述】：
现在，我的链表程序需要一个拐杖才能有效地工作。我需要从 (0,0,null) 节点开始链接列表，因为我的 addToFront() 方法的空头条件不起作用。有人可以帮我解决这个问题吗？我需要消除零，以便以后更容易使用程序，这个小问题给我带来了数小时的痛苦。我知道这一定是失去参考的问题，请帮助我！
add() 方法的输出当前是正确的，因为我已经实现了一个拐杖方法来杀死多项式的零节点，但我真的想知道我的 addToFront() 方法做错了什么。这是最底层的方法，我知道 if(head==null) 部分失败了，因为如果我没有初始化列表的第一个节点并因此绕过它，我会返回一个空列表。非常感谢您提前提供的帮助！
public Polynomial add(Polynomial p)
{
Polynomial newPoly = new Polynomial();
newPoly.poly = new Node(0,0,null);
Node curr = this.poly;
Node curr2 = p.poly;
float co;
int deg;
while(curr!=null && curr2!=null)
{
if(curr.term.degree == curr2.term.degree)
{
co = curr.term.coeff + curr2.term.coeff;
deg = curr.term.degree;
curr=curr.next;
curr2=curr2.next;
}
else if(curr.term.degree > curr2.term.degree)
{
co=curr.term.coeff;
deg = curr.term.degree;
curr=curr.next;
}
else
{
co=curr2.term.coeff;
deg=curr2.term.degree;
curr2=curr2.next;
}
if(co!=0)
{
addToFront(co,deg,newPoly.poly);
}
// addToBack(co,deg,newPoly.poly);
// System.out.println(newPoly.poly.term.coeff);
}
while(curr!=null)
{
co=curr.term.coeff;
deg=curr.term.degree;
curr=curr.next;
if(co!=0)
{
addToFront(co,deg,newPoly.poly);
}
}
while(curr2!=null)
{
co=curr2.term.coeff;
deg=curr2.term.degree;
curr2=curr2.next;
if(co!=0)
{
addToFront(co,deg,newPoly.poly);
}
}
System.out.println("Addition completed");
killFirst(newPoly);
newPoly = reverse(newPoly);
killFirst(newPoly);
return newPoly;
}
/**
* Returns the polynomial obtained by multiplying the given polynomial p
* with this polynomial - DOES NOT change this polynomial
*
* @param p Polynomial with which this polynomial is to be multiplied
* @return A new polynomial which is the product of this polynomial and p.
*/
public Polynomial multiply(Polynomial p)
{
Polynomial newPoly = new Polynomial();
newPoly.poly = new Node(0,0,null);
Node curr = this.poly;
Node curr2 = p.poly;
Polynomial tempPoly = new Polynomial();
//for(curr=this.poly;curr!=null;curr=curr.next)
while(curr!=null)
{
float x1 = curr.term.coeff;
int y1 = curr.term.degree;
tempPoly.poly = new Node(0,0,null);
while(curr2!=null)
{
float x2 = curr2.term.coeff;
int y2 = curr2.term.degree;
addToFront(x1*x2, y1+y2, tempPoly.poly);
newPoly = newPoly.add(tempPoly);
curr2=curr2.next;
}
curr=curr.next;
}
return newPoly;
}
/**
* Evaluates this polynomial at the given value of x
*
* @param x Value at which this polynomial is to be evaluated
* @return Value of this polynomial at x
*/
public Polynomial reverse(Polynomial p)
{
Polynomial newPoly = new Polynomial();
newPoly.poly = new Node(p.poly.term.coeff,p.poly.term.degree,newPoly.poly);
while(p.poly!=null)
{
addToFront(p.poly.term.coeff,p.poly.term.degree,newPoly.poly);
p.poly=p.poly.next;
}
return newPoly;
}
public void killFirst(Polynomial p)
{
p.poly = p.poly.next;
}
public float evaluate(float x)
{
Node curr = this.poly;
int hornerCount = 1;
float horner = x;
float sum = 0;
while(curr!=null)
{
if(curr.term.degree==0)
{
sum = sum + curr.term.coeff;
}
else if(curr.term.degree==1)
{
sum = sum+(curr.term.coeff*horner);
}
else if(curr.term.degree>hornerCount)
{
for(int i=0;i<curr.term.degree-hornerCount;i++)
{
horner = horner*x;
}
System.out.println("horner ="+horner);
sum = sum+(curr.term.coeff*horner);
hornerCount = curr.term.degree;
}
curr=curr.next;
System.out.println("+ "+sum);
}
return sum;
}
/* (non-Javadoc)
* @see java.lang.Object#toString()
*/
public String toString() {
String retval;
if (poly == null) {
return "0";
} else {
retval = poly.term.toString();
for (Node current = poly.next ;
current != null ;
current = current.next) {
retval = current.term.toString() + " + " + retval;
}
return retval;
}
}
private void sort(Node head) // CURRENTLY BROKEN!!!!!!!!!!
{
Node temp;
Node prev;
Node curr = head;
while(curr.next != null)
{
if(curr.term.degree < curr.next.term.degree) // deg is smaller or greater
{//swap
temp = curr; //save first element
curr = curr.next; //set first element to second
temp.next = curr.next; //set next of first to third
curr.next = temp; //set second element to the first that we saved before
}
prev = curr;
curr = curr.next; //move to next element
}
}
private void addToFront(float coeff, int deg, Node head)
{
// System.out.println("Hello");
if(head==null)
{
System.out.println("List empty, creating new node");
head = new Node(coeff,deg,head);
System.out.println(head.term.coeff);
}
else
{
Node n = new Node(coeff, deg, head.next);
// System.out.println(n.term.coeff + " and "+ n.term.degree);
head.next = n;
}
}
【问题讨论】：
-
创建哨兵头节点能解决问题吗？
标签： java linked-list