LeetCode-Reverse Words in a String

Posted 2020-11-01 IncredibleThings

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Given an input string, reverse the string word by word.

Example:  

Input: "the sky is blue",
Output: "blue is sky the".

Notes:

• A word is defined as a sequence of non-space characters.
• Input string may contain leading or trailing spaces. However, your reversed string should not contain leading or trailing spaces.
• You need to reduce multiple spaces between two words to a single space in the reversed string.

Follow up: For C programmers, try to solve it in-place in O(1) space.

 

 

用 stack 做

public class Solution {
    public String reverseWords(String s) {
        if(s == null || s.length() == 0){
            return s;
        }
        Stack<String> stack = new Stack<>();
        StringBuilder sb = new StringBuilder();
        for(int i=0; i<s.length(); i++){
            char c = s.charAt(i);
            if(c != ‘ ‘){
                sb.append(c);
            }
            if((i == s.length() - 1 || c == ‘ ‘) && sb.length() != 0){
                stack.push(sb.toString());
                sb.delete(0,sb.length());
            }
        }
        int count = 0;
        while(!stack.isEmpty()){
            if(count == stack.size()-1){
                sb.append(stack.pop());
            }
            else{
                sb.append(stack.pop()+" ");
            }
        }
        return sb.toString();
    }
}