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Reverse Words in a String III

LeetCode 557 | Difficulty: Easy​

Easy

Problem Description​

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

Example 1:

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

Example 2:

Input: s = "Mr Ding"
Output: "rM gniD"

Constraints:

- `1 <= s.length <= 5 * 10^4`

- `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.

Topics: Two Pointers, String

Approach​

Direct Approach​

This problem can typically be solved with straightforward iteration or simple data structure usage. Focus on correctness first, then optimize.

When to use

Basic problems that test fundamental programming skills.

Solutions​

Solution 1: C# (Best: 544 ms)​

MetricValue
Runtime544 ms
MemoryN/A
Date2018-04-04
Solution
public class Solution {
    public string ReverseWords(string s) {
        char[] sArray = s.ToCharArray();
    int n = s.Length;
    
    //reverse(sArray, 0, n-1);
    int i=0;int j=0;
    while(i<n && sArray[i]==' ') i++;
    while(i<n)
    {
        j=i;
        while(j<n && sArray[j]!=' ') j++;
        reverse(sArray,i,j-1);
        i=j+1;
    }
    return new string(sArray);
    
    
}
void reverse(char[] ar, int l, int r)
{
    while (l < r)
    {
        char temp = ar[l];
        ar[l] = ar[r];
        ar[r] = temp;
        l++;
        r--;
    }
}
}

Complexity Analysis​

ApproachTimeSpace
Two Pointers$O(n)$$O(1)$

Interview Tips​

Key Points
  • Start by clarifying edge cases: empty input, single element, all duplicates.