# Check if a number N starts with 1 in b-base

Given a number N and base b if N in base b representation starts with 1 print Yes else print No
Examples :

```Input : n = 6, b = 4
Output : Yes
6 can be written as in base 4
so answer is Yes as it starts with 1

Input : n = 24, b = 2
Output : Yes
24 can be written as in base 2
so answer is Yes as it starts with 1

Input :  n = 24, b = 7
Output : No
24 can be written as in base 7
so answer is No as it starts with 3
```

## Recommended: Please solve it on “PRACTICE ” first, before moving on to the solution.

When a number N is represented in base ‘b’ it gets converted to m+1 length sequence  ….. which implies * + * …..+ * = N
The smallest number in base b and starting with ‘1’ i.e. 100..00 and m+1 digits in base is and largest number is 2* -1.So N should lie in this range. <= N <= 2* -1
Now another thing to notice is that m cannot exceed floor( (N)) because when we represent any number in base-2 it gets converted into a sequence of only 1s and 0s so the length of this sequence will always be greater than any other base representation and its length will be equal to floor( (N))+1.
So to check for a given base 'b' if N starts with 1 or not we will traverse from m = 1 to m = floor( (N)) and check if for any m N lies in the range <= N <= 2* -1 or not and accordingly print "Yes" or "No".

## C++

 `// C++ program to check if number starts with ` `// one in base b representation ` `#include ` `using` `namespace` `std; ` ` `  `// Returns true if n starts with  1 in ` `// base b represenation ` `bool` `CheckIfstartsWithOne(``int` `n, ``int` `b) ` `{ ` `    ``// highest m can be log2(n) ` `    ``int` `m = log2(n); ` `    ``for` `(``int` `i = 1; i <= m; i++) { ` `        ``// if b^m <= N <= 2*b^m - 1, ` `        ``// return true ` `        ``if` `(n >= ``pow``(b, i) && n <= 2 * ``pow``(b, i) - 1) ` `            ``return` `true``; ` `    ``} ` `    ``return` `false``; ` `} ` ` `  `// printing yes or no ` `void` `printYesORno(``int` `n, ``int` `b) ` `{ ` `    ``if` `(CheckIfstartsWithOne(n, b) == ``true``) ` `        ``cout << ``"Yes"` `<< endl; ` `    ``else` `if` `(CheckIfstartsWithOne(n, b) == ``false``) ` `        ``cout << ``"No"` `<< endl; ` `} ` ` `  `// driver function ` `int` `main() ` `{ ` `    ``printYesORno(6, 4); ` `    ``printYesORno(24, 2); ` `    ``printYesORno(24, 7); ` `    ``printYesORno(24, 15); ` `} `

## Java

 `// Java program to check if number starts with ` `// one in base b representation ` ` `  `class` `GFG { ` `     `  `    ``// Returns true if n starts with 1 in ` `    ``// base b represenation ` `    ``static` `boolean` `CheckIfstartsWithOne(``int` `n, ``int` `b) ` `    ``{ ` `         `  `        ``// highest m can be log2(n) ` `        ``int` `m = (``int``)(Math.log10(n) / Math.log10(``2``)); ` `        ``for` `(``int` `i = ``1``; i <= m; i++) { ` `             `  `            ``// if b^m <= N <= 2*b^m - 1, ` `            ``// return true ` `            ``if` `(n >= (``int``)Math.pow(b, i) && ` `                ``n <= ``2` `* (``int``)Math.pow(b, i) - ``1``) ` `                ``return` `true``; ` `        ``} ` `         `  `        ``return` `false``; ` `    ``} ` ` `  `    ``// Driver method ` `    ``public` `static` `void` `main(String args[]) ` `    ``{ ` `        ``System.out.println( ` `           ``CheckIfstartsWithOne(``6``, ``4``) ? ``"Yes"` `: ``"No"``); ` `            `  `        ``System.out.println( ` `           ``CheckIfstartsWithOne(``24``, ``2``) ? ``"Yes"` `: ``"No"``); ` `            `  `        ``System.out.println( ` `           ``CheckIfstartsWithOne(``24``, ``7``) ? ``"Yes"` `: ``"No"``); ` `            `  `        ``System.out.println( ` `           ``CheckIfstartsWithOne(``24``, ``15``) ? ``"Yes"` `: ``"No"``); ` `    ``} ` `} `

## Python3

 `# Python3 program to check  ` `# if number starts with one ` `# in base b representation ` `import` `math ` ` `  `# Returns true if n  ` `# starts with 1 in  ` `# base b represenation ` `def` `CheckIfstartsWithOne(n, b): ` `     `  `    ``# highest m can be log2(n) ` `    ``m ``=` `(``int``)(math.log2(n)); ` `    ``for` `i ``in` `range` `(``1``, m ``+` `1``): ` `         `  `        ``# if b^m <= N <= 2*b^m - 1, ` `        ``#return true ` `        ``x ``=` `(``int``)(math.``pow``(b, i)); ` `        ``if` `n >``=` `x ``and` `n <``=` `2` `*` `x ``-` `1``: ` `            ``return` `1``; ` `    ``return` `0``; ` ` `  `# printing yes or no ` `def` `printYesORno(n, b): ` `    ``if` `CheckIfstartsWithOne(n, b) ``=``=` `1``: ` `        ``print``(``"Yes"``); ` `    ``if` `CheckIfstartsWithOne(n, b) ``=``=` `0``: ` `        ``print``(``"No"``); ` `         `  `# Driver Code ` `printYesORno(``6``, ``4``); ` `printYesORno(``24``, ``2``); ` `printYesORno(``24``, ``7``); ` `printYesORno(``24``, ``15``); ` ` `  `# This code is contributed by mits. `

## C#

 `// C# program to check if number starts ` `// with one in base b representation ` `using` `System; ` ` `  `public` `class` `GFG { ` `     `  `    ``// Returns true if n starts with ` `    ``// 1 in base b represenation ` `    ``static` `bool` `CheckIfstartsWithOne(``int` `n, ``int` `b) ` `    ``{ ` `         `  `        ``// highest m can be log2(n) ` `        ``int` `m = (``int``)(Math.Log10(n) / Math.Log10(2)); ` `         `  `        ``for` `(``int` `i = 1; i <= m; i++) ` `        ``{ ` `             `  `            ``// if b^m <= N <= 2*b^m - 1, ` `            ``// return true ` `            ``if` `(n >= (``int``)Math.Pow(b, i) &&  ` `                   ``n <= 2 * (``int``)Math.Pow(b, i) - 1) ` `                ``return` `true``; ` `        ``} ` `         `  `        ``return` `false``; ` `    ``} ` ` `  `    ``// Driver method ` `    ``public` `static` `void` `Main() ` `    ``{ ` `        ``Console.WriteLine( ` `           ``CheckIfstartsWithOne(6, 4) ? ``"Yes"` `: ``"No"``); ` `            `  `        ``Console.WriteLine( ` `           ``CheckIfstartsWithOne(24, 2) ? ``"Yes"` `: ``"No"``); ` `            `  `        ``Console.WriteLine( ` `           ``CheckIfstartsWithOne(24, 7) ? ``"Yes"` `: ``"No"``); ` `            `  `        ``Console.WriteLine( ` `           ``CheckIfstartsWithOne(24, 15) ? ``"Yes"` `: ``"No"``); ` `    ``} ` `} ` ` `  `// This code is contributed by Sam007. `

## PHP

 `= pow(``\$b``, ``\$i``) &&  ` `                ``\$n` `<= 2 * pow(``\$b``, ``\$i``) - 1) ` `            ``return` `true; ` `    ``} ` `    ``return` `false; ` `} ` ` `  `// printing yes or no ` `function` `printYesORno(``\$n``, ``\$b``) ` `{ ` `    ``if` `(CheckIfstartsWithOne(``\$n``, ``\$b``) == true) ` `        ``echo` `"Yes"` `,``"\n"``; ` `    ``else` `if` `(CheckIfstartsWithOne(``\$n``, ``\$b``) == false) ` `        ``echo` `"No"` `,``"\n"``; ` `} ` ` `  `// Driver Code ` `printYesORno(6, 4); ` `printYesORno(24, 2); ` `printYesORno(24, 7); ` `printYesORno(24, 15); ` ` `  `// This code is contributed by ajit  ` `?> `

Output :

```Yes
Yes
No
Yes
```

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Improved By : Sam007, jit_t, Mithun Kumar

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