Leetcode: String 04 (reverse the words in the string)

151. Flip the words in the string

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Given a string , Flip each word in the string one by one .

Example 1：
Input : “the sky is blue”
Output : “blue is sky the”

Example 2：
Input : " hello world! "
Output : “world! hello”
explain : The input string can contain extra spaces before or after , But the reversed characters cannot include .

Example 3：
Input : “a good example”
Output : “example good a”
explain : If there are extra spaces between two words , Reduce the space between inverted words to just one .

As soon as this question is brought , I don't think it's easy

    public static String reverseWords(String s) {
    
        StringBuilder result = new StringBuilder("");
        s = s.trim();
        String[] strs = s.split(" ");
        for (int i = strs.length - 1; i > 0; i--) {
    
            // Prevent contiguous spaces 
            if (!"".equals(strs[i])) {
    
                result.append(strs[i]).append(" ");
            }
        }
        // The last digit without spaces 
        result.append(strs[0]);
        return String.valueOf(result);
    }

Take a brief look at the solution

So finally, in order to make this question meaningful , I did it again according to the idea of solving the problem

package com.programmercarl.string;

/** * @ClassName ReverseWords * @Descriotion TODO * @Author nitaotao * @Date 2022/6/25 14:30 * @Version 1.0 * https://leetcode.cn/problems/reverse-words-in-a-string/ * 151.  Invert words in string  **/
public class ReverseWords {
    
    public static void main(String[] args) {
    
        System.out.println(reverseWords("the sky is blue"));
    }
    /** *  Don't use java Built in method  * 1  Remove more than spaces  * 2  Reverse string  * 3  Reverse words  * * @param s * @return */
    public static String reverseWords(String s) {
    
        StringBuilder result;
        // Remove extra space 
        result = removeSpace(s);
        // Invert the entire string 
        result = reverseStr(result, 0, result.length());
        // Invert each word 
        int start = 0;
        int end = 0;
        for (int i = 0; i < result.length(); i++) {
    
            if (result.charAt(end) == ' ') {
    
                result = reverseStr(result, start, end);
                end++;
                start = end;
            } else {
    
                end++;
            }
        }
        // Reverse the last word 
        result = reverseStr(result, start, result.length());
        return String.valueOf(result);
    }

    /** *  Remove extra space  * * @param s * @return */
    public static StringBuilder removeSpace(String s) {
    
        StringBuilder result = new StringBuilder("");
        char[] strs = s.toCharArray();
        for (int i = 0; i < strs.length; i++) {
    
            // Determine whether it is a space in the header 
            if (strs[0] == ' ' && i == 0) {
    
                continue;
            }
            // Determine whether there are more spaces in the middle 
            if (strs[i] == ' ' && strs[i - 1] == ' ') {
    
                continue;
            }
            result.append(strs[i]);
        }
        // Determine whether the last digit is a space 
        if (result.charAt(result.length() - 1) == ' ') {
    
            result.deleteCharAt(result.length() - 1);
        }
        return result;
    }

    /** *  Inverts the string in the specified interval  * * @param s * @param start * @param end * @return */
    public static StringBuilder reverseStr(StringBuilder s, int start, int end) {
    
        while (start < end) {
    
            char temp = s.charAt(start);
            s.replace(start, start + 1, String.valueOf(s.charAt(end - 1)));
            s.replace(end - 1, end, String.valueOf(temp));
            start++;
            end--;
        }
        return s;
    }
}

Although the result is not very good-looking , But after all, this question makes sense , Remain true to our original aspiration .