# Check whether given string can be generated after concatenating given strings

Given three strings str, A and B. The task is to check whether str = A + B or str = B + A where + denotes concatenation.

Examples:

Input: str = “GeeksforGeeks”, A = “Geeksfo”, B = “rGeeks”
Output: Yes
str = A + B = “Geeksfo” + “rGeeks” = “GeeksforGeeks”

Input: str = “Delhicapitals”, B = “Delmi”, C = “capitals”
Output: No

## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Approach:

1. If len(str) != len(A) + len(B) then it is not possible to generate str by concatenating a + b or b + a.
2. Else check whether str starts with a and ends with b or it starts with b and ends with a. Print Yes if any of these is true else print No

Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach ` `#include ` `using` `namespace` `std; ` ` `  `// Function that return true ` `// if pre is a prefix of str ` `bool` `startsWith(string str, string pre) ` `{ ` `    ``int` `strLen = str.length(); ` `    ``int` `preLen = pre.length(); ` `    ``int` `i = 0, j = 0; ` ` `  `    ``// While there are characters to match ` `    ``while` `(i < strLen && j < preLen) { ` ` `  `        ``// If characters differ at any position ` `        ``if` `(str[i] != pre[j]) ` `            ``return` `false``; ` `        ``i++; ` `        ``j++; ` `    ``} ` ` `  `    ``// str starts with pre ` `    ``return` `true``; ` `} ` ` `  `// Function that return true ` `// if suff is a suffix of str ` `bool` `endsWith(string str, string suff) ` `{ ` `    ``int` `i = str.length() - 0; ` `    ``int` `j = suff.length() - 0; ` ` `  `    ``// While there are characters to match ` `    ``while` `(i >= 0 && j >= 0) { ` ` `  `        ``// If characters differ at any position ` `        ``if` `(str[i] != suff[j]) ` `            ``return` `false``; ` `        ``i--; ` `        ``j--; ` `    ``} ` ` `  `    ``// str ends with suff ` `    ``return` `true``; ` `} ` ` `  `// Function that returns true ` `// if str = a + b or str = b + a ` `bool` `checkString(string str, string a, string b) ` `{ ` ` `  `    ``// str cannot be generated ` `    ``// by concatenating a and b ` `    ``if` `(str.length() != a.length() + b.length()) ` `        ``return` `false``; ` ` `  `    ``// If str starts with a ` `    ``// i.e. a is a prefix of str ` `    ``if` `(startsWith(str, a)) { ` ` `  `        ``// Check if the rest of the characters ` `        ``// are equal to b i.e. b is a suffix of str ` `        ``if` `(endsWith(str, b)) ` `            ``return` `true``; ` `    ``} ` ` `  `    ``// If str starts with b ` `    ``// i.e. b is a prefix of str ` `    ``if` `(startsWith(str, b)) { ` ` `  `        ``// Check if the rest of the characters ` `        ``// are equal to a i.e. a is a suffix of str ` `        ``if` `(endsWith(str, a)) ` `            ``return` `true``; ` `    ``} ` ` `  `    ``return` `false``; ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``string str = ``"GeeksforGeeks"``; ` `    ``string a = ``"Geeksfo"``; ` `    ``string b = ``"rGeeks"``; ` ` `  `    ``if` `(checkString(str, a, b)) ` `        ``cout << ``"Yes"``; ` `    ``else` `        ``cout << ``"No"``; ` ` `  `    ``return` `0; ` `} `

## Java

 `// Java implementation of the approach ` `import` `java.util.*; ` ` `  `class` `GFG ` `{  ` `     `  `// Function that return true ` `// if pre is a prefix of str ` `static` `boolean` `startsWith(String str, String pre) ` `{ ` `    ``int` `strLen = str.length(); ` `    ``int` `preLen = pre.length(); ` `    ``int` `i = ``0``, j = ``0``; ` ` `  `    ``// While there are characters to match ` `    ``while` `(i < strLen && j < preLen)  ` `    ``{ ` ` `  `        ``// If characters differ at any position ` `        ``if` `(str.charAt(i) != pre.charAt(j)) ` `            ``return` `false``; ` `        ``i++; ` `        ``j++; ` `    ``} ` ` `  `    ``// str starts with pre ` `    ``return` `true``; ` `} ` ` `  `// Function that return true ` `// if suff is a suffix of str ` `static` `boolean` `endsWith(String str, String suff) ` `{ ` `    ``int` `i = str.length() - ``1``; ` `    ``int` `j = suff.length() - ``1``; ` ` `  `    ``// While there are characters to match ` `    ``while` `(i >= ``0` `&& j >= ``0``)  ` `    ``{ ` ` `  `        ``// If characters differ at any position ` `        ``if` `(str.charAt(i) != suff.charAt(j)) ` `            ``return` `false``; ` `        ``i--; ` `        ``j--; ` `    ``} ` ` `  `    ``// str ends with suff ` `    ``return` `true``; ` `} ` ` `  `// Function that returns true ` `// if str = a + b or str = b + a ` `static` `boolean` `checkString(String str, String a, String b) ` `{ ` ` `  `    ``// str cannot be generated ` `    ``// by concatenating a and b ` `    ``if` `(str.length() != a.length() + b.length()) ` `        ``return` `false``; ` ` `  `    ``// If str starts with a ` `    ``// i.e. a is a prefix of str ` `    ``if` `(startsWith(str, a))  ` `    ``{ ` ` `  `        ``// Check if the rest of the characters ` `        ``// are equal to b i.e. b is a suffix of str ` `        ``if` `(endsWith(str, b)) ` `            ``return` `true``; ` `    ``} ` ` `  `    ``// If str starts with b ` `    ``// i.e. b is a prefix of str ` `    ``if` `(startsWith(str, b))  ` `    ``{ ` ` `  `        ``// Check if the rest of the characters ` `        ``// are equal to a i.e. a is a suffix of str ` `        ``if` `(endsWith(str, a)) ` `            ``return` `true``; ` `    ``} ` ` `  `    ``return` `false``; ` `} ` ` `  `// Driver code ` `public` `static` `void` `main(String args[]) ` `{ ` `    ``String str = ``"GeeksforGeeks"``; ` `    ``String a = ``"Geeksfo"``; ` `    ``String b = ``"rGeeks"``; ` ` `  `    ``if` `(checkString(str, a, b)) ` `        ``System.out.println(``"Yes"``); ` `    ``else` `        ``System.out.println(``"No"``); ` ` `  `} ` `} ` ` `  `// This code is contributed by Arnab Kundu `

## Python3

 `# Python3 implementation of the approach  ` ` `  `# Function that return true  ` `# if pre is a prefix of str  ` `def` `startsWith(``str``, pre): ` `    ``strLen ``=` `len``(``str``) ` `    ``preLen ``=` `len``(pre) ` `    ``i ``=` `0` `    ``j ``=` `0` `     `  `    ``# While there are characters to match  ` `    ``while` `(i < strLen ``and` `j < preLen): ` `         `  `        ``# If characters differ at any position  ` `        ``if` `(``str``[i] !``=` `pre[j]) : ` `            ``return` `False` `        ``i ``+``=` `1` `        ``j ``+``=` `1` `         `  `    ``# str starts with pre  ` `    ``return` `True` `     `  `# Function that return true  ` `# if suff is a suffix of str  ` `def` `endsWith(``str``, suff): ` `    ``i ``=` `len``(``str``) ``-` `1` `    ``j ``=` `len``(suff) ``-` `1` `     `  `    ``# While there are characters to match  ` `    ``while` `(i >``=` `0` `and` `j >``=` `0``): ` `         `  `        ``# If characters differ at any position  ` `        ``if` `(``str``[i] !``=` `suff[j]): ` `            ``return` `False` `        ``i ``-``=` `1` `        ``j ``-``=` `1` `     `  `    ``# str ends with suff  ` `    ``return` `True` ` `  `# Function that returns true  ` `# if str = a + b or str = b + a  ` `def` `checkString(``str``, a, b): ` `     `  `    ``# str cannot be generated  ` `    ``# by concatenating a and b  ` `    ``if` `(``len``(``str``) !``=` `len``(a) ``+` `len``(b)): ` `        ``return` `False` `         `  `    ``# If str starts with a  ` `    ``# i.e. a is a prefix of str  ` `    ``if` `(startsWith(``str``, a)): ` ` `  `        ``# Check if the rest of the characters  ` `        ``# are equal to b i.e. b is a suffix of str  ` `        ``if` `(endsWith(``str``, b)): ` `            ``return` `True` `     `  `    ``# If str starts with b  ` `    ``# i.e. b is a prefix of str  ` `    ``if` `(startsWith(``str``, b)): ` `         `  `        ``# Check if the rest of the characters  ` `        ``# are equal to a i.e. a is a suffix of str  ` `        ``if` `(endsWith(``str``, a)): ` `            ``return` `True` `     `  `    ``return` `False` `     `  `# Driver code  ` `str` `=` `"GeeksforGeeks"` `a ``=` `"Geeksfo"` `b ``=` `"rGeeks"` ` `  `if` `(checkString(``str``, a, b)): ` `    ``print``(``"Yes"``) ` `else``: ` `    ``print``(``"No"``) ` ` `  `# This code is contributed by SHUBHAMSINGH10 `

## C#

 `// C# implementation of the approach ` `using` `System; ` ` `  `class` `GFG ` `{  ` `     `  `// Function that return true ` `// if pre is a prefix of str ` `static` `Boolean startsWith(String str,  ` `                          ``String pre) ` `{ ` `    ``int` `strLen = str.Length; ` `    ``int` `preLen = pre.Length; ` `    ``int` `i = 0, j = 0; ` ` `  `    ``// While there are characters to match ` `    ``while` `(i < strLen && j < preLen)  ` `    ``{ ` ` `  `        ``// If characters differ at any position ` `        ``if` `(str[i] != pre[j]) ` `            ``return` `false``; ` `        ``i++; ` `        ``j++; ` `    ``} ` ` `  `    ``// str starts with pre ` `    ``return` `true``; ` `} ` ` `  `// Function that return true ` `// if suff is a suffix of str ` `static` `Boolean endsWith(String str,  ` `                        ``String suff) ` `{ ` `    ``int` `i = str.Length - 1; ` `    ``int` `j = suff.Length - 1; ` ` `  `    ``// While there are characters to match ` `    ``while` `(i >= 0 && j >= 0)  ` `    ``{ ` ` `  `        ``// If characters differ at any position ` `        ``if` `(str[i] != suff[j]) ` `            ``return` `false``; ` `        ``i--; ` `        ``j--; ` `    ``} ` ` `  `    ``// str ends with suff ` `    ``return` `true``; ` `} ` ` `  `// Function that returns true ` `// if str = a + b or str = b + a ` `static` `Boolean checkString(String str,  ` `                           ``String a,  ` `                           ``String b) ` `{ ` ` `  `    ``// str cannot be generated ` `    ``// by concatenating a and b ` `    ``if` `(str.Length != a.Length + b.Length) ` `        ``return` `false``; ` ` `  `    ``// If str starts with a ` `    ``// i.e. a is a prefix of str ` `    ``if` `(startsWith(str, a))  ` `    ``{ ` ` `  `        ``// Check if the rest of the characters ` `        ``// are equal to b i.e. b is a suffix of str ` `        ``if` `(endsWith(str, b)) ` `            ``return` `true``; ` `    ``} ` ` `  `    ``// If str starts with b ` `    ``// i.e. b is a prefix of str ` `    ``if` `(startsWith(str, b))  ` `    ``{ ` ` `  `        ``// Check if the rest of the characters ` `        ``// are equal to a i.e. a is a suffix of str ` `        ``if` `(endsWith(str, a)) ` `            ``return` `true``; ` `    ``} ` ` `  `    ``return` `false``; ` `} ` ` `  `// Driver code ` `public` `static` `void` `Main(String []args) ` `{ ` `    ``String str = ``"GeeksforGeeks"``; ` `    ``String a = ``"Geeksfo"``; ` `    ``String b = ``"rGeeks"``; ` ` `  `    ``if` `(checkString(str, a, b)) ` `        ``Console.WriteLine(``"Yes"``); ` `    ``else` `        ``Console.WriteLine(``"No"``); ` `} ` `} ` ` `  `// This code is contributed by 29AjayKumar `

## PHP

 `= 0 && ``\$j` `>= 0)  ` `    ``{  ` ` `  `        ``// I\$f characters differ at any position  ` `        ``if` `(``\$str``[``\$i``] != ``\$suff``[``\$j``])  ` `            ``return` `false;  ` `        ``\$i``--;  ` `        ``\$j``--;  ` `    ``}  ` ` `  `    ``// str ends with suff  ` `    ``return` `true;  ` `}  ` ` `  `// Function that returns true  ` `// if str = a + b or str = b + a  ` `function` `checkString(``\$str``, ``\$a``, ``\$b``)  ` `{  ` ` `  `    ``// str cannot be generated  ` `    ``// by concatenating a and b  ` `    ``if` `(``strlen``(``\$str``) != ``strlen``(``\$a``) + ``strlen``(``\$b``)) ` `        ``return` `false;  ` ` `  `    ``// If str starts with a  ` `    ``// i.e. a is a prefix of str  ` `    ``if` `(startsWith(``\$str``, ``\$a``))  ` `    ``{  ` ` `  `        ``// Check if the rest of the characters  ` `        ``// are equal to b i.e. b is a suffix of str  ` `        ``if` `(endsWith(``\$str``, ``\$b``))  ` `            ``return` `true;  ` `    ``}  ` ` `  `    ``// If str starts with b  ` `    ``// i.e. b is a prefix of str  ` `    ``if` `(startsWith(``\$str``, ``\$b``))  ` `    ``{  ` ` `  `        ``// Check if the rest of the characters  ` `        ``// are equal to a i.e. a is a suffix of str  ` `        ``if` `(endsWith(``\$str``, ``\$a``))  ` `            ``return` `true;  ` `    ``}  ` ` `  `    ``return` `false;  ` `}  ` ` `  `// Driver code  ` `\$str` `= ``"GeeksforGeeks"``;  ` `\$a` `= ``"Geeksfo"``;  ` `\$b` `= ``"rGeeks"``;  ` ` `  `if` `(checkString(``\$str``, ``\$a``, ``\$b``))  ` `    ``echo` `"Yes"``;  ` `else` `    ``echo` `"No"``;  ` ` `  `// This code is contributed by AnkitRai01 ` `?> `

Output:

```Yes
```

Time Complexity: O(N)

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