#include <math.h>
#include <stdlib.h>
#include "poly.h"

struct poly *polyCreate() {
	// initialize empty list
	return (struct poly *)0;
}

struct poly *polyDelete(struct poly *p) {
	while(p) {
		struct poly *temp = p; // remember current node
		p = p->p; // move to next node
		free(temp); // delete current node
	}

	return p;
}

double polyEval(struct poly *p, double x) {
	double f = 0.0;

	// iterate over linked list and evaluate each term
	for( ; p; p = p->p)
		f += p->a * pow(x, (double)p->n);

	return f;
}

struct poly *polySetCoefficient(struct poly *p, int degree, double value) {
	// empty list or insert at head
	if(!p || p->n < degree) {
		struct poly *q = malloc(sizeof(struct poly));
		q->a = value;
		q->n = degree;
		q->p = p;
		return q;
	}

	// find place to insert
	// cur points to node after which new node to come
	struct poly *cur = p;
	while(cur->p && cur->p->n > degree) cur = cur->p;

	// node of degree n already present
	if(cur->p && cur->p->n == degree)
		cur->p->a = value;
	// new node needed
	else {
		struct poly *q = malloc(sizeof(struct poly));
		q->a = value;
		q->n = degree;
		// insert into linked list
		q->p = cur->p;
		cur->p = q;
	}

	return p;
}

double polyGetCoefficient(struct poly *p, int degree) {
	for( ; p && p->n > degree; p = p->p) ;

	if(!p || p->n != degree) return 0.0;
	else return p->a;
}