# Check if string follows order of characters defined by a pattern or not | Set 1

• Difficulty Level : Medium
• Last Updated : 04 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
Explanation:
All 'e' in the input string are before all 'r'.

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

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

The idea is very simple. For every pair (x, y) of consecutive characters in the pattern string, we find the last occurrence of x and first occurrence of y in the input string. If last occurrence of character x is after first occurrence of character y for any pair, we return false. Checking for every pair of consecutive characters in the pattern string will suffice. For example, if we consider three consecutive characters in the pattern say x, y and z, if (x, y) and (y, z) returns true, that implies (x, z) is also true.

Below is the implementation of above idea

## C++

 `// C++ program check if characters in the input string``// follows the same order as determined by characters``// present in the given pattern``#include ``using` `namespace` `std;`` ` `// Function to check if characters in the input string``// follows the same order as determined by characters``// present in the given pattern``bool` `checkPattern(string str, string pattern)``{``    ``// len stores length of the given pattern``    ``int` `len = pattern.length();``     ` `    ``// if length of pattern is more than length of``    ``// input string, return false;``    ``if` `(str.length() < len)``        ``return` `false``;``     ` `    ``for` `(``int` `i = 0; i < len - 1; i++)``    ``{``        ``// x, y are two adjacent characters in pattern``        ``char` `x = pattern[i];``        ``char` `y = pattern[i + 1];``        ` `        ``// find index of last occurrence of character x``        ``// in the input string``        ``size_t` `last = str.find_last_of(x);``         ` `        ``// find index of first occurrence of character y``        ``// in the input string``        ``size_t` `first = str.find_first_of(y);``         ` `        ``// return false if x or y are not present in the``        ``// input string OR last occurrence of x is after``        ``// the first occurrence of y in the input string``        ``if` `(last == string::npos || first == ``            ``string::npos || last > first)   ``        ``return` `false``;``    ``}``     ` `    ``// return true if string matches the pattern``    ``return` `true``;``}` `// Driver code``int` `main()``{``    ``string str = ``"engineers rock"``;``    ``string pattern = ``"gsr"``;`` ` `    ``cout << boolalpha << checkPattern(str, pattern);`` ` `    ``return` `0;``}`

## Java

 `// Java program check if characters in the input string``// follows the same order as determined by characters``// present in the given pattern` `class` `GFG``{` `    ``// Function to check if characters in the input string``    ``// follows the same order as determined by characters``    ``// present in the given pattern``    ``static` `boolean` `checkPattern(String str, String pattern)``    ``{``        ``// len stores length of the given pattern``        ``int` `len = pattern.length();` `        ``// if length of pattern is more than length of``        ``// input string, return false;``        ``if` `(str.length() < len)``        ``{``            ``return` `false``;``        ``}` `        ``for` `(``int` `i = ``0``; i < len - ``1``; i++)``        ``{``            ``// x, y are two adjacent characters in pattern``            ``char` `x = pattern.charAt(i);``            ``char` `y = pattern.charAt(i + ``1``);` `            ``// find index of last occurrence of character x``            ``// in the input string``            ``int` `last = str.lastIndexOf(x);` `            ``// find index of first occurrence of character y``            ``// in the input string``            ``int` `first = str.indexOf(y);` `            ``// return false if x or y are not present in the``            ``// input string OR last occurrence of x is after``            ``// the first occurrence of y in the input string``            ``if` `(last == -``1` `|| first``                    ``== -``1` `|| last > first)``            ``{``                ``return` `false``;``            ``}``        ``}` `        ``// return true if string matches the pattern``        ``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 contributed by Rajput-Ji`

## Python3

 `# Python3 program check if characters in``# the input string follows the same order``# as determined by characters present in``# the given pattern` `# Function to check if characters in the``# input string follows the same order as``# determined by characters present``# in the given pattern``def` `checkPattern(string, pattern):` `    ``# len stores length of the given pattern``    ``l ``=` `len``(pattern)` `    ``# if length of pattern is more than length``    ``# of input string, return false;``    ``if` `len``(string) < l:``        ``return` `False` `    ``for` `i ``in` `range``(l ``-` `1``):` `        ``# x, y are two adjacent characters in pattern``        ``x ``=` `pattern[i]``        ``y ``=` `pattern[i ``+` `1``]` `        ``# find index of last occurrence of``        ``# character x in the input string``        ``last ``=` `string.rindex(x)` `        ``# find index of first occurrence of``        ``# character y in the input string``        ``first ``=` `string.index(y)` `        ``# return false if x or y are not present``        ``# in the input string OR last occurrence of``        ``# x is after the first occurrence of y``        ``# in the input string``        ``if` `last ``=``=` `-``1` `or` `first ``=``=` `-``1` `or` `last > first:``            ``return` `False` `    ``# return true if``    ``# string matches the pattern``    ``return` `True` `# Driver Code``if` `__name__ ``=``=` `"__main__"``:``    ``string ``=` `"engineers rock"``    ``pattern ``=` `"gsr"``    ``print``(checkPattern(string, pattern))` `# This code is contributed by``# sanjeev2552`

## C#

 `// C# program check if characters in the input string``// follows the same order as determined by characters``// present in the given pattern``using` `System;``    ` `class` `GFG``{` `    ``// Function to check if characters in the input string``    ``// follows the same order as determined by characters``    ``// present in the given pattern``    ``static` `Boolean checkPattern(String str, String pattern)``    ``{``        ``// len stores length of the given pattern``        ``int` `len = pattern.Length;` `        ``// if length of pattern is more than length of``        ``// input string, return false;``        ``if` `(str.Length < len)``        ``{``            ``return` `false``;``        ``}` `        ``for` `(``int` `i = 0; i < len - 1; i++)``        ``{``            ``// x, y are two adjacent characters in pattern``            ``char` `x = pattern[i];``            ``char` `y = pattern[i+1];` `            ``// find index of last occurrence of character x``            ``// in the input string``            ``int` `last = str.LastIndexOf(x);` `            ``// find index of first occurrence of character y``            ``// in the input string``            ``int` `first = str.IndexOf(y);` `            ``// return false if x or y are not present in the``            ``// input string OR last occurrence of x is after``            ``// the first occurrence of y in the input string``            ``if` `(last == -1 || first``                    ``== -1 || last > first)``            ``{``                ``return` `false``;``            ``}``        ``}` `        ``// return true if string matches the pattern``        ``return` `true``;``    ``}` `    ``// Driver code``    ``public` `static` `void` `Main(String[] args)``    ``{``        ``String str = ``"engineers rock"``;``        ``String pattern = ``"gsr"``;` `        ``Console.WriteLine(checkPattern(str, pattern));``    ``}``}` `/* This code contributed by PrinciRaj1992 */`

## Javascript

 ``

Output

`false`

We have discussed two more approaches to solve this problem.
Check if string follows order of characters defined by a pattern or not | Set 2
Check if string follows order of characters defined by a pattern or not | Set 3

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