/* polyadd.c */
/* 多項式相加--使用降冪排列輸入兩個格式為 ax^b 的多項式相加 */

#include <stdio.h>
#include <stdlib.h>

struct poly {
    int coef;   /* 多項式係數 */
    int exp;    /* 多項式指數 */
    struct poly *next;
};

void input(struct poly *, struct poly *, struct poly *);  /* 輸入函數 */
void poly_add(void);         /* 多項式相加函數 */
void show_ans(void);         /* 顯示多項式相加結果函數 */
void display_func(struct poly *, struct poly *);
void flushBuffer(void);

struct poly *ptr,  *ans_h;
struct poly *head1, *this_n1, *prev1, *eq_h1;
struct poly *head2, *this_n2, *prev2, *eq_h2;

int main()
{
    head1=(struct poly *) malloc(sizeof(struct poly));
    head1->next = NULL;
    head2=(struct poly *) malloc(sizeof(struct poly));
    head2->next = NULL;

    printf("****************************************\n");
    printf(" -- Polynomial format is ax^b --\n");
    printf("****************************************\n");
    printf("Please enter the first equation, terminate at -1\n");
    input(prev1, head1, this_n1);
    printf("Please enter the second equation, terminate at -1\n");
    input(prev2, head2, this_n2);
    poly_add();
    show_ans();

    return 0;
}

void input(struct poly *prev, struct poly *head, struct poly *this_n)
{
    do {
        ptr = (struct poly *) malloc(sizeof(struct poly));
        ptr->next = NULL;
        /* 取得輸入資料 */
        printf("Coefficient: ");
        scanf("%d", &ptr->coef);
        flushBuffer();
        printf("Exponential: ");
        scanf("%d", &ptr->exp);
        flushBuffer();

        if (ptr->coef == -1 && ptr->exp == -1) {
            break;
        }

        //插入資料
        prev = head;
        this_n = head->next;
        while ((this_n != NULL) && (this_n->exp > ptr->exp)) {
            prev = this_n;
            this_n = this_n->next;
        }
        ptr->next = this_n;
        prev->next = ptr;
    } while(ptr->exp != -1);
    display_func(this_n, head);
}

void poly_add(void)
{
    struct poly *prev;
    prev = NULL;
    this_n1 = head1->next;
    this_n2 = head2->next;
    /* 當兩個多項式皆相加完畢則結束 */
    while (this_n1 != NULL || this_n2 != NULL) {
        ptr = (struct poly *) malloc(sizeof(struct poly));
        ptr->next = NULL;
        /* 第一個多項式指數大於第二個多項式 */
        if (this_n1 != NULL && (this_n2 == NULL
                           || this_n1->exp > this_n2->exp)) {
            ptr->coef = this_n1->coef;
            ptr->exp = this_n1->exp;
            this_n1 = this_n1->next;
        }
        else {
            /* 第一個多項式指數小於第二個多項式 */
            if (this_n1 == NULL || this_n1->exp < this_n2->exp) {
                ptr->coef = this_n2->coef;
                ptr->exp = this_n2->exp;
                this_n2 = this_n2->next;
            }
            else {  /* 兩個多項式指數相等，進行相加 */
                ptr->coef = this_n1->coef + this_n2->coef;
                ptr->exp = this_n1->exp;
                if(this_n1 != NULL)
                    this_n1 = this_n1->next;
                if(this_n2 != NULL)
                    this_n2 = this_n2->next;
            }
        }
        if(ptr->coef != 0) {  /* 當相加結果不等於0，則放入答案多項式中 */
            if(ans_h == NULL)
                ans_h = ptr;
            else
                prev->next = ptr;
            prev = ptr;
        }
        else free(ptr);
    }
}

void show_ans(void)
{
    struct poly *this_n;
    this_n = ans_h;
    printf("The equation: ");
    while(this_n != NULL) {
        printf("%dx^%d", this_n->coef, this_n->exp);
        if(this_n->next != NULL && this_n->next->coef >= 0)
            printf("+");
        this_n = this_n->next;
    }
    printf("\n");
}

void display_func(struct poly *this_n, struct poly *head)
{
    int count=0;
    if (head->next == NULL) {
        printf(" No item in polynominal\n");
    }
    else {
        printf("\n  coef      exp\n");
        printf(" -----------------\n");
        this_n=head->next;
        while (this_n != NULL) {
            printf("  %-7d %3d\n", this_n->coef, this_n->exp);
            count++;
            this_n=this_n->next;
        }
        printf(" -----------------\n");
        printf(" Total %d item(s) found\n\n", count);
    }
}

void flushBuffer()
{
    while(getchar() != '\n') {
        continue;
    }
}