2022.05.29 (lc_6079_price reduction)

  Method ： simulation

import java.text.DecimalFormat;
class Solution {
    public String discountPrices(String sentence, int discount) {
        String[] str = sentence.split(" ");
        for (int i = 0; i < str.length; i++) {
            if (satisfy(str[i])) {
                java.text.DecimalFormat df = new java.text.DecimalFormat("#0.00");
                double num = Double.valueOf(str[i].substring(1, str[i].length()));
                num = num - (num * ((double)discount / 100));
                str[i] = '$' + df.format(num);
            }
        }
        String ans = "";
        for (int i = 0; i < str.length; i++) {
            if (i != str.length - 1) {
                ans += str[i] + " ";
            } else {
                ans += str[i];
            }
        }
        return ans;
    }
    public boolean satisfy(String s) {
        if (s.charAt(0) != '$') return false;
        if (s.charAt(s.length() - 1) == '$') return false;
        int count$ = 0, countD = 0, countC = 0;
        for (char ch : s.toCharArray()) {
            if (ch == '$') {
                count$++;
            } else if (Character.isDigit(ch)) {
                countD++;
            } else {
                countC++;
            }
        }
        if (count$ != 1 || countC > 0) return false;
        return true;
    }
}

class Solution {
    public String discountPrices(String sentence, int discount) {
        String[] s = sentence.split(" ");
        for (int i = 0; i < s.length; i++) {
            if (satisfy(s[i])) {
                double num = Double.valueOf(s[i].substring(1));
                num = num * (1 - (double)discount / 100);
                s[i] = "$" + String.format("%.2f", num);
            }
        }
        return String.join(" ", s);
    }
    // Judge whether the word is price ( Words meet the conditions ： The first is $, Other bits are numbers )
    public boolean satisfy(String s) {
        if (s.charAt(0) != '$' || s.length() == 1) return false;
        for (int i = 1; i < s.length(); i++) {
            if (s.charAt(i) < '0' || s.charAt(i) > '9') {
                return false;
            }
        }
        return true;
    }
}

Use library functions ：String.format(),String.join().