Valid Discount Coupons Amazon OA Solution

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Valid Discount Coupons Amazon OA Solution

At Amazon’s annual sale, employees are tasked with generating valid discount coupons for loyal customers. However, there are some used/invalid coupons in the mix, and the challenge in this task is to determine whether a given discount coupon is valid or not.

The validity of a discount coupon is determined as follows:

  1. An empty discount coupon is valid.
  2. If a discount coupon A is valid, then a discount coupon C made by adding one character xto both the beginning of A
    and the end of A is also valid (i.e the discount coupon C = xAx is valid).
  3. If two discount coupons A and Bare valid, then the concatenation of B and A is also valid
    (i.e the coupons AB and BA are both valid).

Given n discount coupons, each coupon consisting of only lowercase English characters,

where the i-th discount coupon is denoted discounts[i], determine if each discount coupon is valid or not.

A valid coupon is denoted by 1 in the answer array while an invalid coupon is denoted by 0.


discounts = [‘tabba’; ‘abca’]

Check if this coupon code can be constructed within the rules of a valid coupon.

Checking ‘abba’:

• The empty string is valid per the first rule.

• Under the second rule, the same character can be added to the beginning and end of a valid coupon code.

Add ‘b’ to the beginning and end of the empty string to have ‘bb’, a valid code.

• Using the same rule, ‘a’ is added to the beginning and end of the ‘bb’ coupon string. Again, the string is valid.

The string is valid, so the answer array is [1].

Checking ‘abca’:

• Using rule 2, a letter can be added to both ends of a string without altering its validity.

The ‘a’ added to the beginning and end of ‘bc’ does not change its validity.

• The remaining string ‘Ix’, is not valid. There is no rule allowing the addition of different characters to the ends of a string.

Since the string is invalid, append 0 to the answer array. There are no more strings to test, so return [1,0]

Function Description

Complete the function find ValidDiscountCoupons in the editor below.

find ValidDiscountCoupons has the following parameter:

string discounts[n]: the discount coupons to validate


int[n]: each element i is 1 if the coupon discounts[il is valid and 0 otherwise

Valid Discount Coupons Amazon OA
Valid Discount Coupons Amazon OA Solution


Program: Valid Discount Coupons Amazon OA Solution in Python

def findCoupons(discounts):
	result = []
	for discount in discounts:
		if discount[0] == discount[-1]:
			discount = discount[1:-1]
		result.append(1 if finddiscountPattern(discount)else 0)
	return result
def finddiscountPattern(discount):
	mostleft = 0
	left = 1
	while left < len(discount):
		if discount[mostleft] == discount[left]:
			discount = discount[:mostleft]+discount[left+1:]
			mostleft = 0
			left = 1
			mostleft += 1
			left += 1
	if not len(discount):
		return True
	return False

Program: Valid Discount Coupons Amazon OA Solution in Java

public class Main {
    public static void main(String[] args) {
        List<String> discount = List.of("abba", "abca", "abbacbbc", "aabb", "xaaxybbyzccz", "vaas", "jay");
        // Expected O/P - [1, 0, 1, 1, 1, 0, 0]
        List<Integer> list = findDiscounts(discount);
        // TC - O(n * k), n--> length of the array input & k --> length of each string in input array
        // SC - O(n) - no DS used other than to store response
    private static List<Integer> findDiscounts(List<String> discount) {
        List<Integer> result = new ArrayList<>();
        for (String str : discount) {
            if (str.equals("")) {
                // Condition #1
            } else if (str.length() %2 != 0) {
                // String has to be even length as per given condition, else its invalid coupon
            } else if (isPalindrome(str)) {
                // If string is even length and palindrome, its valid!
            } else if (isPalindrome(findPalindromicPart(str, true)) && 
                      isPalindrome(findPalindromicPart(str, false))) {
                // We can also have concatenation of 2 even palindromes (condition #3) which are valid!
            } else {
        return result;
    private static boolean isPalindrome(String str) {
        if (str == null || str.trim().equals("")) return false;
        int start = 0, end = str.length()-1;
        while (start < end) {
            if (str.charAt(start) != str.charAt(end)) {
                return false;
        return true;
    private static String findPalindromicPart(String str, boolean findLeftPart) {
        // We need to extract palindrome part - it can either be on left side or right side 
        // of the string. So we need to check both.
        // Hence we have this findLeftPart boolean variable
        // We could have simplified this and have 2 functions instead - one for finding 
        // left and other for finding right side palindrome, but that would cause duplicate lines of code
        int start = 0, end = str.length()-1;
        StringBuilder result = new StringBuilder("");
        while (start < end) {
            if (str.charAt(start) == str.charAt(end)) {
            } else if (str.charAt(start) != str.charAt(end)) {
                if (findLeftPart)
        return result.toString() + result.reverse().toString();

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