Interview Classic 150 Questions P151 Reverse Words in a String

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Timeline

Timeline

2025-11-09

init

stringstream

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Problem:

P151 Reverse Words in a String

https://leetcode.cn/problems/reverse-words-in-a-string/description/?envType=study-plan-v2&envId=top-interview-150

stringstream

Use stringstream to get each word:

#include <sstream>
#include <stack>
#include <string>

using std::stringstream;
using std::string;
using std::stack;

class Solution {
    public:
	string reverseWords(string s)
	{
		stack<string> st;
		stringstream ss(s);
		string tmp, res;

		while (ss >> tmp) {
			st.push(tmp);
		}

		while (!st.empty()) {
			tmp = st.top();
			st.pop();
			res += tmp;
			res += " ";
		}
		res.pop_back(); // Remove the last space
		return res;
	}
};

Two pointers

You can also use two pointers

class Solution {
public:
    string reverseWords(string s) {
        // Use two pointers
        int m = s.size() - 1;
        string res;
        // Remove trailing spaces
        while (s[m] == ' ' && m > 0) m--;
        int n = m; // n is another pointer
        while (m >= 0) {
            while (m >= 0 && s[m] != ' ') m--;
            res += s.substr(m + 1, n - m) + " "; // Get the word and add a space
            while (m >= 0 && s[m] == ' ') m--;
            n = m;
        }
        return res.substr(0, res.size() - 1); // ignore the trailing space
    }
};