# Check if string follows order of characters defined by a pattern or not | Set 3

• Difficulty Level : Medium
• Last Updated : 05 Jul, 2022

Given an input string and a pattern, check if characters in the input string follows the same order as determined by characters present in the pattern. Assume there won’t be any duplicate characters in the pattern.

Examples:

```Input: string = "engineers rock", pattern = "er";
Output: true
All 'e' in the input string are before all 'r'.

Input: string = "engineers rock", pattern = "egr";
Output: false
There are two 'e' after 'g' in the input string.

Input: string = "engineers rock", pattern = "gsr";
Output: false
There are one 'r' before 's' in the input string.```

We have discussed two approaches to solve this problem.
Check if string follows order of characters defined by a pattern or not | Set 1
Check if string follows order of characters defined by a pattern or not | Set 2

In this approach we first assign a label (or order) to characters of pattern. The labels are assigned in increasing order.

For example, the pattern “gsr” is labeled as following

```"g" => 1
"s" => 2
"r" => 3```

It means ‘g’ will come first, then ‘s’, then ‘r’
After assigning labels to pattern characters, we iterate through string characters. While traversing, we keep track of label (or order) of last visited character. If label of current character is less than previous character, we return false. Otherwise we update last label. If all characters follow order, we return true.

Below is the implementation

## C++

 `// C++ program to find if a string follows order``// defined by a given pattern.``#include ``using` `namespace` `std;` `const` `int` `CHAR_SIZE = 256;` `// Returns true if characters of str follow``// order defined by a given ptr.``bool` `checkPattern(string str, string pat)``{``    ``// Initialize all orders as -1``    ``vector<``int``> label(CHAR_SIZE, -1);` `    ``// Assign an order to pattern characters``    ``// according to their appearance in pattern``    ``int` `order = 1;``    ``for` `(``int` `i = 0; i < pat.length() ; i++)``    ``{``        ``// give the pattern characters order``        ``label[pat[i]] = order;` `        ``// increment the order``        ``order++;``    ``}` `    ``//  Now one by check if string characters``    ``// follow above order``    ``int` `last_order = -1;``    ``for` `(``int` `i = 0; i < str.length(); i++)``    ``{``        ``if` `(label[str[i]] != -1)``        ``{``            ``// If order of this character is less``            ``// than order of previous, return false.``            ``if` `(label[str[i]] < last_order)``                ``return` `false``;` `            ``// Update last_order for next iteration``            ``last_order =  label[str[i]];``        ``}``    ``}` `    ``// return that str followed pat``    ``return` `true``;``}` `// Driver code``int` `main()``{``    ``string str = ``"engineers rock"``;``    ``string pattern = ``"gsr"``;` `    ``cout << boolalpha << checkPattern(str, pattern);` `    ``return` `0;``}`

## Java

 `// Java program to find if a string follows order``// defined by a given pattern.``class` `GFG``{``    ``static` `int` `CHAR_SIZE = ``256``;` `    ``// Returns true if characters of str follow``    ``// order defined by a given ptr.``    ``static` `boolean` `checkPattern(String str,``                                ``String pat)``    ``{``        ``int``[] label = ``new` `int``[CHAR_SIZE];` `        ``// Initialize all orders as -1``        ``for` `(``int` `i = ``0``; i < CHAR_SIZE; i++)``            ``label[i] = -``1``;` `        ``// Assign an order to pattern characters``        ``// according to their appearance in pattern``        ``int` `order = ``1``;``        ``for` `(``int` `i = ``0``; i < pat.length(); i++)``        ``{` `            ``// give the pattern characters order``            ``label[pat.charAt(i)] = order;` `            ``// increment the order``            ``order++;``        ``}` `        ``// Now one by check if string characters``        ``// follow above order``        ``int` `last_order = -``1``;``        ``for` `(``int` `i = ``0``; i < str.length(); i++)``        ``{``            ``if` `(label[str.charAt(i)] != -``1``)``            ``{` `                ``// If order of this character is less``                ``// than order of previous, return false.``                ``if` `(label[str.charAt(i)] < last_order)``                    ``return` `false``;` `                ``// Update last_order for next iteration``                ``last_order = label[str.charAt(i)];``            ``}``        ``}` `        ``// return that str followed pat``        ``return` `true``;``    ``}` `    ``// Driver code``    ``public` `static` `void` `main(String[] args)``    ``{``        ``String str = ``"engineers rock"``;``        ``String pattern = ``"gsr"``;``        ``System.out.println(checkPattern(str, pattern));``    ``}``}` `// This code is contributed by``// sanjeev2552`

## Python3

 `# Python3 program to find if a string follows``# order defined by a given pattern``CHAR_SIZE ``=` `256` `# Returns true if characters of str follow``# order defined by a given ptr.``def` `checkPattern(``Str``, pat):` `    ``# Initialize all orders as -1``    ``label ``=` `[``-``1``] ``*` `CHAR_SIZE` `    ``# Assign an order to pattern characters``    ``# according to their appearance in pattern``    ``order ``=` `1``    ` `    ``for` `i ``in` `range``(``len``(pat)):` `        ``# Give the pattern characters order``        ``label[``ord``(pat[i])] ``=` `order` `        ``# Increment the order``        ``order ``+``=` `1` `    ``# Now one by one check if string``    ``# characters follow above order``    ``last_order ``=` `-``1``    ` `    ``for` `i ``in` `range``(``len``(``Str``)):``        ``if` `(label[``ord``(``Str``[i])] !``=` `-``1``):` `            ``# If order of this character is less``            ``# than order of previous, return false``            ``if` `(label[``ord``(``Str``[i])] < last_order):``                ``return` `False` `            ``# Update last_order for next iteration``            ``last_order ``=` `label[``ord``(``Str``[i])]` `    ``# return that str followed pat``    ``return` `True` `# Driver Code``if` `__name__ ``=``=` `'__main__'``:``    ` `    ``Str` `=` `"engineers rock"``    ``pattern ``=` `"gsr"` `    ``print``(checkPattern(``Str``, pattern))` `# This code is contributed by himanshu77`

## C#

 `// C# program to find if a string follows order``// defined by a given pattern.``using` `System;` `class` `GFG``{``    ``static` `int` `CHAR_SIZE = 256;` `    ``// Returns true if characters of str follow``    ``// order defined by a given ptr.``    ``static` `bool` `checkPattern(String str,``                                ``String pat)``    ``{``        ``int``[] label = ``new` `int``[CHAR_SIZE];` `        ``// Initialize all orders as -1``        ``for` `(``int` `i = 0; i < CHAR_SIZE; i++)``            ``label[i] = -1;` `        ``// Assign an order to pattern characters``        ``// according to their appearance in pattern``        ``int` `order = 1;``        ``for` `(``int` `i = 0; i < pat.Length; i++)``        ``{` `            ``// give the pattern characters order``            ``label[pat[i]] = order;` `            ``// increment the order``            ``order++;``        ``}` `        ``// Now one by check if string characters``        ``// follow above order``        ``int` `last_order = -1;``        ``for` `(``int` `i = 0; i < str.Length; i++)``        ``{``            ``if` `(label[str[i]] != -1)``            ``{` `                ``// If order of this character is less``                ``// than order of previous, return false.``                ``if` `(label[str[i]] < last_order)``                    ``return` `false``;` `                ``// Update last_order for next iteration``                ``last_order = label[str[i]];``            ``}``        ``}` `        ``// return that str followed pat``        ``return` `true``;``    ``}` `    ``// Driver code``    ``public` `static` `void` `Main(String[] args)``    ``{``        ``String str = ``"engineers rock"``;``        ``String pattern = ``"gsr"``;``        ``Console.WriteLine(checkPattern(str, pattern));``    ``}``}` `// This code is contributed by 29AjayKumar`

## Javascript

 ``

Output

`false`

Time Complexity of this program is O(n) with constant extra space (the array label is of constant size, 256).

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