Invert a vowel in a string

Write a function that takes a string as input and inverts the vowels in the string.

Examples can be found on the LeetCode website.

Source: LeetCode link: leetcode-cn.com/problems/re… Copyright belongs to the Collar buckle network. Commercial reprint please contact official authorization, non-commercial reprint please indicate the source.

Solution 1: stack in reverse order

  • First initialize the vowels list.

  • Then loop through each character in s, placing the vowels in turn on the stack;

  • Then loop s again, replace the vowel letter with the top element of the stack;

  • When the loop is complete, the string is reversed.

import java.util.ArrayList;
import java.util.List;
import java.util.Stack;

public class LeetCode_345 {
    /** * list of vowels */
    private static List<Character> vowels = new ArrayList<>();

    static {
        // Initialize all vowels
        vowels.add('a');
        vowels.add('e');
        vowels.add('i');
        vowels.add('o');
        vowels.add('u');
        vowels.add('A');
        vowels.add('E');
        vowels.add('I');
        vowels.add('O');
        vowels.add('U');
    }

    public static String reverseVowels(String s) {
        if (s == null || s.length() < 2) {
            return s;
        }

        char[] sList = s.toCharArray();
        Stack<Character> vowelStack = new Stack<>();
        for (char c : sList) {
            if (vowels.contains(c)) {
                // Put vowels on the stackvowelStack.push(c); }}for (int i = 0; i < sList.length; i++) {
            if (vowels.contains(sList[i])) {
                // Remove vowels from stack, in reverse ordersList[i] = vowelStack.pop(); }}return new String(sList);
    }

    public static void main(String[] args) {
        System.out.println(reverseVowels("hello")); }}Copy the code

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