19. Strings (LB)

Character Array-

1. We use 1d character array to simulate strings, e.g.,

char ch[10];
cin>>ch;
2. string ends with '\0'
3. cin with string works only if till space, tab or new line is absent in input...

4. work with character array just like a normal array, here only datatype is changed to char, else wise it is just an array
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5. In-Built functions-

- int n = strlen(ch)  

- strcmp(s1,s2)            // gives 0 if both strings are equal 

- strcpy(dest,source)   // copies a string from dest to source

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STRING-

It is a C++ STL

1. has dynamic size (can dynamically increase size when needed)

2. null terminator (\0) NOT required

3. Has built-in functions:
- return s.size()
- return s == "hello"

- return s + "world"
- return s1.find(s2)      // checks if given string has a substring or not, we get a starting idx                                         from where substring s2 is found in string s1, if not found it returns                                          string::npos
- s.erase(pos, len)       // erase a substring
- s.push_back(ch)
- s.pop_back()
- s.insert(pos,ch)
- s.substr(pos,len)
- stoi(s)

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1. Reverse a sentence-

the sky is blue --> blue is sky the

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2. Find maximum occurring alphabet in a string

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3. Removing substring from a string-

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                            4. Check if s1 is any permutation of s2

Brute- sort both the strings and see if they are equal strings or not (nlogn)

Optimal- check if they have same character frequencies (n)

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      5. Check if any SUBSTRING of s1 is a permutation of s2

SLIDING WINDOW approach
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1. Count frequency of characters in s1 (smaller string)
2. Traverse s2 (larger string) using a window of size = len(s1)
3. Maintain another frequency array for current window
4. If both freq arrays match → permutation found

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