Reverse Words

PROBLEM

Given a string s, reverse the order of characters in each word within a sentence while still preserving whitespace and initial word order.

Example1

*Input*: s = "Let's take LeetCode contest"
*Output*: "s'teL ekat edoCteeL tsetnoc"

Example2

*Input*: s = "God Ding"
*Output*: "diG gniD"

Constraints

  • 1<=s.length<=5*104
  • s contains printable ASCII characters.
  • s does not contain any leading or trailing spaces.
  • There is at least one word in s.
  • All the words in s are separated by a single space.

SOLVING

we’ll use the Two Pointers method

Steps

  • Left and Right Pointer begin at 0
  • Loop until Right Pointer at the last element:
    • Move Right Pointer until the Right+1 = ’ ’ (space)
    • Reverse the word from Left and Right Pointer

Code

class Solution {
public:
  string reverseWords(string s) {
    int rightPtr = 0;
    int leftPtr = 0;
    int size = s.size();

    while (rightPtr < size) {
      while (rightPtr + 1 < size && s[rightPtr + 1] != ' ')
	rightPtr++;
      reverseString(s, leftPtr, rightPtr);
      rightPtr += 2;
      leftPtr = rightPtr;
    }
    return s;
  }

private:
  void reverseString(string &s, int leftPtr, int rightPtr) {
    while (leftPtr < rightPtr) {
      swap(s[leftPtr], s[rightPtr]);
      leftPtr++;
      rightPtr--;
    }
  }
};