# Generate an alternate increasing and decreasing Array

Given a string str of size N containing two types of character only that are “I” or “D”. The task is to generate an array arr[0, 1, . . N] of size N + 1 sattisfing the following conditions:

• If str[i] == “I”   then   arr[i] < arr[i+1]
• If str[i] == “D”  then  arr[i] > arr[i+1]

Examples:

Input: str = “IDID”
Output: 0 4 1 3 2
Explaination:
str == “I” therfore arr < arr
str == “D” therfore arr > arr
str == “I” therfore arr < arr
str == “D” therfore arr > arr
Input: str = “III”
Output: 0 1 2 3

Approach:

1. Initialize variable START as 0 and END as N.
2. Iterate over the entire array.
3. If str[i] == “I”  then assign START at arr[i] and Increment the START.
4. If str[i] == “D” then assign END at arr[i] and Decrement the END.
5. Now the last element of the array isn’t assigned so assign START at A[N].

Below is the implementation of the approach.

 `// C++ program to Generate an increasing ` `// and decreasing array ` ` `  `#include ` `using` `namespace` `std; ` ` `  `// Function that returns generated array ` `int``* DiStirngMatch(string Str) ` `{ ` `    ``int` `N = Str.length(); ` ` `  `    ``// Dynamically allocate array ` `    ``int``* arr = ``new` `int``[N]; ` ` `  `    ``// START=0, END=N ` `    ``int` `START = 0, END = N; ` ` `  `    ``// iterate over array ` `    ``for` `(``int` `i = 0; i < N; i++) { ` ` `  `        ``// if Str[i]=='I' assign arr[i] ` `        ``// as START and increment START ` `        ``if` `(Str[i] == ``'I'``) ` `            ``arr[i] = START++; ` ` `  `        ``// if str[i]=='D' assign arr[i] ` `        ``// as END and decrement END ` `        ``if` `(Str[i] == ``'D'``) ` `            ``arr[i] = END--; ` `    ``} ` ` `  `    ``// assign A[N] as START ` `    ``arr[N] = START; ` ` `  `    ``// return starting ` `    ``// address of array A ` `    ``return` `arr; ` `} ` ` `  `// Driver Program ` `int` `main() ` `{ ` `    ``string Str = ``"IDID"``; ` `    ``int` `N = Str.length(); ` `    ``int``* ptr = DiStirngMatch(Str); ` `    ``for` `(``int` `i = 0; i <= N; i++) ` `        ``cout << ptr[i] << ``" "``; ` ` `  `    ``return` `0; ` `} `

 `// Java program to generate an increasing ` `// and decreasing array ` `class` `GFG{ ` ` `  `// Function that returns generated array ` `static` `int` `[]DiStirngMatch(String Str) ` `{ ` `    ``int` `N = Str.length(); ` ` `  `    ``// Dynamically allocate array ` `    ``int` `[]arr = ``new` `int``[N + ``1``]; ` ` `  `    ``// START=0, END=N ` `    ``int` `START = ``0``, END = N; ` ` `  `    ``// Iterate over array ` `    ``for``(``int` `i = ``0``; i < N; i++) ` `    ``{ ` `         `  `        ``// if Str[i]=='I' assign arr[i] ` `        ``// as START and increment START ` `        ``if` `(Str.charAt(i) == ``'I'``) ` `            ``arr[i] = START++; ` ` `  `        ``// if str[i]=='D' assign arr[i] ` `        ``// as END and decrement END ` `        ``if` `(Str.charAt(i) == ``'D'``) ` `            ``arr[i] = END--; ` `    ``} ` ` `  `    ``// Assign A[N] as START ` `    ``arr[N] = START; ` ` `  `    ``// Return starting ` `    ``// address of array A ` `    ``return` `arr; ` `} ` ` `  `// Driver code ` `public` `static` `void` `main(String[] args) ` `{ ` `    ``String Str = ``"IDID"``; ` `    ``int` `N = Str.length(); ` `    ``int``[] ptr = DiStirngMatch(Str); ` `     `  `    ``for``(``int` `i = ``0``; i <= N; i++) ` `        ``System.out.print(ptr[i] + ``" "``); ` `} ` `} ` ` `  `// This code is contributed by amal kumar choubey `

 `# Python3 program to generate an  ` `# increasing and decreasing array ` ` `  `# Function that returns generated array ` `def` `DiStirngMatch(``Str``): ` ` `  `    ``N ``=` `len``(``Str``) ` ` `  `    ``# Dynamically allocate array ` `    ``arr ``=` `(N ``+` `1``) ``*` `[``0``] ` ` `  `    ``# START, END= 0 ,N ` `    ``START, END ``=` `0``, N ` ` `  `    ``# Iterate over array ` `    ``for` `i ``in` `range` `(N): ` ` `  `        ``# If Str[i]=='I' assign arr[i] ` `        ``# as START and increment START ` `        ``if` `(``Str``[i] ``=``=` `'I'``): ` `            ``arr[i] ``=` `START ` `            ``START ``+``=` `1` ` `  `        ``# If str[i]=='D' assign arr[i] ` `        ``# as END and decrement END ` `        ``if` `(``Str``[i] ``=``=` `'D'``): ` `            ``arr[i] ``=` `END ` `            ``END ``-``=` `1` ` `  `    ``# Assign A[N] as START ` `    ``arr[N] ``=` `START ` `     `  `    ``# Return starting ` `    ``# address of array A ` `    ``return` `arr ` ` `  `# Driver code ` `if` `__name__ ``=``=` `"__main__"``: ` ` `  `    ``Str` `=` `"IDID"` `    ``N ``=` `len``(``Str``) ` `    ``ptr ``=` `DiStirngMatch(``Str``) ` `     `  `    ``for` `i ``in` `range` `(N ``+` `1``): ` `        ``print``(ptr[i], end ``=` `" "``) ` ` `  `# This code is contributed by chitranayal `

 `// C# program to generate an increasing ` `// and decreasing array ` `using` `System; ` ` `  `class` `GFG{ ` ` `  `// Function that returns generated array ` `static` `int` `[]DiStirngMatch(String Str) ` `{ ` `    ``int` `N = Str.Length; ` ` `  `    ``// Dynamically allocate array ` `    ``int` `[]arr = ``new` `int``[N + 1]; ` ` `  `    ``// START=0, END=N ` `    ``int` `START = 0, END = N; ` ` `  `    ``// Iterate over array ` `    ``for``(``int` `i = 0; i < N; i++) ` `    ``{ ` `         `  `        ``// if Str[i]=='I' assign arr[i] ` `        ``// as START and increment START ` `        ``if` `(Str[i] == ``'I'``) ` `            ``arr[i] = START++; ` ` `  `        ``// if str[i]=='D' assign arr[i] ` `        ``// as END and decrement END ` `        ``if` `(Str[i] == ``'D'``) ` `            ``arr[i] = END--; ` `    ``} ` ` `  `    ``// Assign A[N] as START ` `    ``arr[N] = START; ` ` `  `    ``// Return starting ` `    ``// address of array A ` `    ``return` `arr; ` `} ` ` `  `// Driver code ` `public` `static` `void` `Main(String[] args) ` `{ ` `    ``String Str = ``"IDID"``; ` `    ``int` `N = Str.Length; ` `    ``int``[] ptr = DiStirngMatch(Str); ` `     `  `    ``for``(``int` `i = 0; i <= N; i++) ` `        ``Console.Write(ptr[i] + ``" "``); ` `} ` `} ` ` `  `// This code is contributed by amal kumar choubey `

Output:
```0 4 1 3 2
```

Time Complexity: O (N)
Auxiliary Space: O (N)

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