Print longest palindrome word in a sentence in C Program

In C programming, finding the longest palindrome word in a sentence involves parsing individual words and checking if they read the same forwards and backwards. A palindrome is a word that remains identical when its characters are reversed.

What is a Palindrome?

A palindrome is a word or sequence that reads the same backward as forward. For example, "malayalam" is a palindrome because reversing it gives "malayalam" − the same word.

Examples of palindromes: radar, level, madam, racecar

Syntax

int isPalindrome(char word[], int start, int end);
void findLongestPalindrome(char sentence[]);

Algorithm

The algorithm works by extracting each word from the sentence and checking if it's a palindrome using two pointers −

1. Initialize variables for tracking longest palindrome
2. For each character in the sentence:
   - Extract the current word
   - Check if the word is a palindrome using two pointers
   - If palindrome length > current max, update the longest
3. Print the longest palindrome found

Example

Here's a complete program to find the longest palindrome word in a sentence −

#include <stdio.h>
#include <string.h>

int isPalindrome(char word[], int start, int end) {
    while (start < end) {
        if (word[start] != word[end]) {
            return 0;  // Not a palindrome
        }
        start++;
        end--;
    }
    return 1;  // Is a palindrome
}

int main() {
    char str[] = "malayalam liemadameil iji radar";
    int i, k, l, j, maxLen = 0, index = -1, wordLen = 0;
    
    for (i = 0; i < strlen(str); i++) {
        // Skip spaces
        if (str[i] == ' ') continue;
        
        k = i;  // Start of word
        j = i;
        
        // Find end of current word
        while (str[j] != ' ' && str[j] != '\0') {
            j++;
        }
        
        l = j - 1;  // End of word
        wordLen = l - k + 1;
        
        // Check if current word is palindrome
        if (isPalindrome(str, k, l) && wordLen > maxLen) {
            maxLen = wordLen;
            index = k;
        }
        
        i = j - 1;  // Move to end of current word
    }
    
    printf("Longest palindrome word: ");
    if (index != -1) {
        for (i = index; str[i] != ' ' && str[i] != '\0'; i++) {
            printf("%c", str[i]);
        }
    } else {
        printf("No palindrome found");
    }
    printf("<br>");
    
    return 0;
}

Longest palindrome word: liemadameil

How It Works

The program uses these key steps:

• Word Extraction: Identifies word boundaries by finding spaces or null terminators
• Palindrome Check: Uses two pointers moving inward to compare characters
• Length Tracking: Keeps track of the longest palindrome found so far
• Index Storage: Remembers the starting position of the longest palindrome

Key Points

• The algorithm has O(n*m) time complexity where n is sentence length and m is average word length
• Space complexity is O(1) as it uses only a few variables
• Handles multiple palindromes by keeping track of the longest one

Conclusion

This approach efficiently finds the longest palindrome word by checking each word individually using the two-pointer technique. The program handles edge cases and provides a clear solution for palindrome detection in sentences.