LeetCode-in-Java

2288. Apply Discount to Prices

Medium

A sentence is a string of single-space separated words where each word can contain digits, lowercase letters, and the dollar sign '$'. A word represents a price if it is a sequence of digits preceded by a dollar sign.

• For example, "$100", "$23", and "$6" represent prices while "100", "$", and "$1e5" do not.

You are given a string sentence representing a sentence and an integer discount. For each word representing a price, apply a discount of discount% on the price and update the word in the sentence. All updated prices should be represented with exactly two decimal places.

Return a string representing the modified sentence.

Note that all prices will contain at most 10 digits.

Example 1:

Input: sentence = “there are $1 $2 and 5$ candies in the shop”, discount = 50

Output: “there are $0.50 $1.00 and 5$ candies in the shop”

Explanation:

The words which represent prices are “$1” and “$2”.

• A 50% discount on “$1” yields “$0.50”, so “$1” is replaced by “$0.50”.

• A 50% discount on “$2” yields “$1”. Since we need to have exactly 2 decimal places after a price, we replace “$2” with “$1.00”.

Example 2:

Input: sentence = “1 2 $3 4 $5 $6 7 8$ $9 $10$”, discount = 100

Output: “1 2 $0.00 4 $0.00 $0.00 7 8$ $0.00 $10$”

Explanation:

Applying a 100% discount on any price will result in 0.

The words representing prices are “$3”, “$5”, “$6”, and “$9”.

Each of them is replaced by “$0.00”.

Constraints:

• 1 <= sentence.length <= 105
• sentence consists of lowercase English letters, digits, ' ', and '$'.
• sentence does not have leading or trailing spaces.
• All words in sentence are separated by a single space.
• All prices will be positive numbers without leading zeros.
• All prices will have at most 10 digits.
• 0 <= discount <= 100

Solution

public class Solution {
    public String discountPrices(String sentence, int discount) {
        String[] words = sentence.split(" ");
        StringBuilder sb = new StringBuilder();
        for (String word : words) {
            sb.append(applyDiscount(word, discount));
            sb.append(" ");
        }
        sb.deleteCharAt(sb.length() - 1);
        return sb.toString();
    }

    private String applyDiscount(String s, int discount) {
        if (s.charAt(0) == '$' && s.length() > 1) {
            long price = 0;
            for (int i = 1; i < s.length(); i++) {
                if (!Character.isDigit(s.charAt(i))) {
                    // Error case. We could also use Long.parseLong() here.
                    return s;
                }
                price *= 10;
                price += (s.charAt(i) - '0') * (100 - discount);
            }
            String stringPrice = String.valueOf(price);
            if (price < 10) {
                return "$0.0" + stringPrice;
            }
            if (price < 100) {
                return "$0." + stringPrice;
            }
            return "$"
                    + stringPrice.substring(0, stringPrice.length() - 2)
                    + "."
                    + stringPrice.substring(stringPrice.length() - 2);
        }
        return s;
    }
}

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