Check to see if the input is a Palindrome using linked list - C Data Structure

C examples for Data Structure:Linked List

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Description

Check to see if the input is a Palindrome using linked list

Demo Code

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

typedef struct node {
    char ch;//w w  w . j  a v a  2s.c o m
    struct node * next;
} Node, *NodePtr;

NodePtr getPhrase();
NodePtr reverseLetters(NodePtr);
int compare(NodePtr, NodePtr);


int main() {
    NodePtr phrase, s1, s2;

    printf("Type a phrase. (To stop, press 'Enter' only): ");
    phrase = getPhrase();

    s1 = reverseLetters(phrase);
    s2 = reverseLetters(s1);
    
    if (compare(s1, s2) == 0) 
       printf("is a palindrome\n");
    else 
       printf("is not a palindrome\n");

}

NodePtr getPhrase() {
    NodePtr top = NULL, last, np;
    char c = getchar();
    while (c != '\n') {
        np = (NodePtr) malloc(sizeof(Node));
        np -> ch = c;
        np -> next = NULL;
        if (top == NULL) top = np;
        else last -> next = np;
        last = np;
        c = getchar();
    }
    return top;
}

NodePtr reverseLetters(NodePtr top) {
    NodePtr rev = NULL, np;
    char c;
    while (top != NULL) {
        c = top -> ch;
        if (isalpha(c)) { // add to new list
            np = (NodePtr) malloc(sizeof(Node));
            np -> ch = tolower(c);
            np -> next = rev;
            rev = np;
        }
        top = top -> next; //go to next character of phrase
    }
    return rev;
}

int compare(NodePtr s1, NodePtr s2) {
    while (s1 != NULL) {
        if (s1 -> ch < s2 -> ch) return -1;
        else if (s1 -> ch > s2 -> ch) return 1;
        s1 = s1 -> next;
        s2 = s2 -> next;
    }
    return 0;
}

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