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案例:利用单链表的基本操作来实现多项式的相加运算
注:和顺序储存结构相比,利用链式存储更加灵活,更适合表示一般的多项式,合并过程的空间复杂度为O(1)。
分析:用链表表示多项式时,每个链表结点存储多项式中的一个非零项,包括系数(coef)和指数(expn)两个数据域以及一个指针域(next)。
对应的数据结构定义为
typedef struct PNode{
float coef;
int expn;
struct PNode *next;
}PNode,*Polynomial;
代码实现
1、创建多项式:
首先要初始化一个空链表,用来表示多项式,然后逐个输入各项,通过比较,找到第一个大于该输入项指数的项,将该输入项插入到此项的前面,这样即可保证多项式链表的有序性。
算法描述:
//单个多项式指数相同时
void CreatePolyn(Polynomial &p,int n){
p = new PNode;
PNode *s , *pre , *q;
// Polynomial s , pre , q;
p->next = NULL;
int i;
for(i = 1;i<=n;++i){
printf("请输入第%d系数和指数:\n",i);
s = new PNode;
cin>>s->coef>>s->expn;
// scanf("%f %d",&s->coef,&s->expn);
pre = p;
q = p->next;
while(q && q->expn<s->expn){
pre = q;
q = q->next;
}
s->next = q;
pre->next = s;
}
}
算法分析:
创建一个n项的多项式,需要执行n次循环,每次循环又都需要从前向后比较输入项与各项的系数,最坏情况下,第n次循环需要做n次比较,因此时间复杂度为O(n^2)。
创建完两个多项式列表后,就可进行多项式的运算了,这里我只写了相加的算法。
2、多项式相加
假设头指针Pa、Pb的单链表分别为A、B两个多项式的存储结构,指针p1、p2分别指向A、B中进行比较的某个结点,则逐一比较两个节点中的指数项,对于指数相同的项,对应系数相加,若和不为零,将其插入到“和多项式”链表中;对于指数不同的项,则通过比较将指数数值较小的项插入到“和多项式”链表中去。
算法描述:
void AddPolyn(Polynomial &Pa, Polynomial &Pb){
PNode *p1 , *p2 , *p3 , *r;
p1 = Pa->next;
p2 = Pb->next;
p3 = Pa;
int sum = 0;
while(p1&&p2){
if(p1->expn == p2->expn){
sum = p1->coef+p2->coef;
if(sum != 0){
p1->coef = sum;
p3->next = p1;
p3 = p1;
p1 = p1->next;
r = p2;
p2 = p2->next;
delete r;
}else{
r = p1;
p1 = p1->next;
delete r;
r = p2;
p2 = p2->next;
delete r;
}
}else if(p1->expn < p2->expn){
p3->next = p1;
p3 = p1;
p1 = p1->next;
}else{
p3->next = p2;
p3 = p2;
p2 = p2->next;
}
}
p3->next = p1?p1:p2;
delete Pb;
PrintPolyn(Pa);
}
算法分析:
假设两个多项式的系数分别为m、n,则该算法的时间复杂度为O(m+n),空间复杂度为O(1)。
完整代码:
#include<stdio.h>
//#include<stdlib.h>
#include<iostream>
//
using namespace std;
typedef struct PNode{
float coef;
int expn;
struct PNode *next;
}PNode,*Polynomial;
//单个多项式指数相同时未进行处理。f(x)=3x^2+4x^2
void CreatePolyn(Polynomial &p,int n){
p = new PNode;
PNode *s , *pre , *q;
// Polynomial s , pre , q;
p->next = NULL;
int i;
for(i = 1;i<=n;++i){
printf("请输入第%d系数和指数:\n",i);
s = new PNode;
cin>>s->coef>>s->expn;
// scanf("%f %d",&s->coef,&s->expn);
pre = p;
q = p->next;
while(q && q->expn<s->expn){
pre = q;
q = q->next;
}
s->next = q;
pre->next = s;
}
}
void PrintPolyn(Polynomial &L){
PNode *p;
p = L->next;
while(p){
printf("%fX^%d+", p->coef,p->expn);
p = p->next;
}
}
void AddPolyn(Polynomial &Pa, Polynomial &Pb){
PNode *p1 , *p2 , *p3 , *r;
p1 = Pa->next;
p2 = Pb->next;
p3 = Pa;
int sum = 0;
while(p1&&p2){
if(p1->expn == p2->expn){
sum = p1->coef+p2->coef;
if(sum != 0){
p1->coef = sum;
p3->next = p1;
p3 = p1;
p1 = p1->next;
r = p2;
p2 = p2->next;
delete r;
}else{
r = p1;
p1 = p1->next;
delete r;
r = p2;
p2 = p2->next;
delete r;
}
}else if(p1->expn < p2->expn){
p3->next = p1;
p3 = p1;
p1 = p1->next;
}else{
p3->next = p2;
p3 = p2;
p2 = p2->next;
}
}
p3->next = p1?p1:p2;
delete Pb;
PrintPolyn(Pa);
}
int main(){
PNode *p1,*p2;
int n1,n2;
printf("请输入p1的项数\n");
scanf("%d",&n1);
CreatePolyn(p1,n1);
printf("请输入p2的项数\n");
scanf("%d",&n2);
CreatePolyn(p2,n2);
AddPolyn(p1,p2);
return 0;
}