Algorithm

To convert the first and last character of any word to uppercase, we can simply traverse the entire string and look for whitespaces. The character before and after any whitespace is last and first character of a word in the string.

Convert first and last index character to uppercase if initially the string character is in lowercase
Convert the characters present before and after whitespaces to uppercase if initially the string character is in lowercase
Return the final updated string.

Code

#include <bits/stdc++.h>
using namespace std;

class Solution {
public:
    // Function to capitalize first and last character of each word
    string capitalizeFirstLast(string s) {
        int n = (int)s.size();
        int start = 0;

        // Traverse the string word by word
        while (start < n) {
            // Skip spaces
            while (start < n && s[start] == ' ')
                start++;

            if (start >= n)
                break;

            int end = start;

            // Find the end of the current word
            while (end < n && s[end] != ' ')
                end++;

            // Capitalize first character if it's lowercase
            if (islower(s[start]))
                s[start] = toupper(s[start]);

            // Capitalize last character if it's lowercase and word length > 1
            if (end - 1 > start && islower(s[end - 1]))
                s[end