# JavaScript - Count all the numbers with unique digits in a range

## JavaScript Math: Exercise-109 with Solution

Write a JavaScript program that accepts a number (n) and counts all numbers with unique digits of length p within a specified range.

Range: 0 <= p < 10n

Example:
When n = 1, numbers with unique digits (10) between 0 and 9 are 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
When n = 2, numbers with unique digits (91) between 0 and 100 are 0,1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 13, 14, 15 …..99 except 11, 22, 33, 44, 55, 66, 77, 88 and 99.

Test Data:
(1) -> 10
(2) -> 91

Sample Solution:

HTML Code:

``````<!DOCTYPE html>
<html>
<meta charset="utf-8">
<title>JavaScript program to Count all numbers with unique digits in a range</title>
<body>

</body>
</html>
```
```

JavaScript Code:

``````function test(n) {
if(n===0){
return 1;
}
var result = 10;
var temp =9;
for(var i=1; i<n; i++){
temp *= 10-i
result+=temp
}
return result;
}
n = 1
console.log("Range: "+n+" to 10")
console.log("Numbers with unique digits in the said range: "+test(n));
n = 2
console.log("Range: "+n+" to 10")
console.log("Numbers with unique digits in the said range: "+test(n));
```
```

Sample Output:

```Range: 1 to 10
Numbers with unique digits in the said range: 10
Range: 2 to 10
Numbers with unique digits in the said range: 91
```

Flowchart: Live Demo:

See the Pen javascript-math-exercise-109 by w3resource (@w3resource) on CodePen.

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## JavaScript: Tips of the Day

Shorten an array using its length property

A great way of shortening an array is by redefining its length property.

```let array = [0, 1, 2, 3, 4, 5, 6, 6, 8, 9]
array.length = 4
// Result: [0, 1, 2, 3]
```

Important to know though is that this is a destructive way of changing the array. This means you lose all the other values that used to be in the array.

Ref: https://bit.ly/2LBj213