String (Level-1)

1) Basic about c++ string

char str[] = "Geeks"; 
string string_name = "Sample String";
//
Internal Representation:
String characters are internally stored as integers. This means:
Characters like 'A' to 'Z' are mapped to integer values 65 to 90.
Characters like 'a' to 'z' are mapped to integer values 97 to 122.
This contiguous mapping helps in programming tasks, such as comparing characters alphabetically. 
For example, 'A' (65) is less than 'B' (66).

2) Check if string is palindrome or not

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

int main() {
    string s;
    cin >> s; // Input the string

    int start = 0;              // Pointer to the beginning of the string
    int end = s.length() - 1;   // Pointer to the end of the string

    // Check for palindrome
    while (start < end) {
        if (s[start] != s[end]) {
            cout << "No";       // Not a palindrome
            return 0;           // Exit the program
        }
        start++;                // Move start pointer forward
        end--;                  // Move end pointer backward
    }

    cout << "Yes";              // The string is a palindrome
    return 0;
}

3) Check for anagram

Problem: Given two strings, check whether two strings are an anagram of each other. 
Two strings are said to be an anagram of each other if they are just permutations of each other. 
That is, the set of characters in both the strings must be the same, only the order of characters 
can be different.
///
///
Method- 1 (sorting)
///
// C++ program to check whether two strings are anagrams
// of each other
#include <bits/stdc++.h>
using namespace std;

/* function to check whether two strings are anagram of
each other */
bool areAnagram(string str1, string str2)
{
    // Get lengths of both strings
    int n1 = str1.length();
    int n2 = str2.length();

    // If length of both strings is not same, then they
    // cannot be anagram
    if (n1 != n2)
        return false;

    // Sort both the strings
    sort(str1.begin(), str1.end());
    sort(str2.begin(), str2.end());

    // Compare sorted strings
    for (int i = 0; i < n1; i++)
        if (str1[i] != str2[i])
            return false;

    return true;
}

// Driver code
int main()
{
    string str1 = "test";
    string str2 = "ttew";

    // Function Call
    if (areAnagram(str1, str2))
        cout << "The two strings are anagram of each other";
    else
        cout << "The two strings are not anagram of each "
                "other";

    return 0;
}
 Time Complexity: O(N*logN)
Auxiliary Space: O(1)
//
//Method- 2 (count characters)
// C++ program to check if two strings
// are anagrams of each other
#include <bits/stdc++.h>
using namespace std;
#define NO_OF_CHARS 256

/* function to check whether two strings are anagram of
each other */
bool areAnagram(char* str1, char* str2)
{
    // Create 2 count arrays and initialize all values as 0
    int count1[NO_OF_CHARS] = { 0 };
    int count2[NO_OF_CHARS] = { 0 };
    int i;

    // For each character in input strings, increment count
    // in the corresponding count array
    for (i = 0; str1[i] && str2[i]; i++) {
        count1[str1[i]]++;
        count2[str2[i]]++;
    }

    // If both strings are of different length. Removing
    // this condition will make the program fail for strings
    // like "aaca" and "aca"
    if (str1[i] || str2[i])
        return false;

    // Compare count arrays
    for (i = 0; i < NO_OF_CHARS; i++)
        if (count1[i] != count2[i])
            return false;

    return true;
}

/* Driver code*/
int main()
{
    char str1[] = "geeksforgeeks";
    char str2[] = "forgeeksgeeks";

    // Function Call
    if (areAnagram(str1, str2))
        cout << "The two strings are anagram of each other";
    else
        cout << "The two strings are not anagram of each "
                "other";

    return 0;
}

Time Complexity : O(n)

Space Complexity : O(NO_OF_CHAR) = O(256) = O(1) (constant space use)

4) Reverse word in given string

// C++ program to reverse a string
#include <bits/stdc++.h>
using namespace std;

// Function to reverse words*/
void reverseWords(string s)
{

    // temporary vector to store all words
    vector<string> tmp;
    string str = "";
    for (int i = 0; i < s.length(); i++) {

        // Check if we encounter space
        // push word(str) to vector
        // and make str NULL
        if (s[i] == ' ') {
            tmp.push_back(str);
            str = "";
        }

        // Else add character to
        // str to form current word
        else
            str += s[i];
    }

    // Last word remaining,add it to vector
    tmp.push_back(str);

    // Now print from last to first in vector
    int i;
    for (i = tmp.size() - 1; i > 0; i--)
        cout << tmp[i] << " ";
    // Last word remaining,print it
    cout << tmp[0] << endl;
}

// Driver Code
int main()
{
    string s = "i like this program very much";
    reverseWords(s);
    return 0;
}