Last updated on October 6th, 2024 at 02:00 pm

Here, We see Count Numbers with Unique Digits LeetCode Solution. This Leetcode problem is done in many programming languages like C++, Java, JavaScript, Python, etc. with different approaches.

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Count Numbers with Unique Digits LeetCode Solution

Problem Statement

Given an integer n, return the count of all numbers with unique digits, x, where 0 <= x < 10ⁿ.

Example 1:
Input: n = 2
Output: 91
Explanation: The answer should be the total numbers in the range of 0 ≤ x < 100, excluding 11,22,33,44,55,66,77,88,99

Example 2:
Input: n = 0
Output: 1

1. Count Numbers with Unique Digits Leetcode Solution C++

class Solution {
public:
    int countNumbersWithUniqueDigits(int n) {
        int sum = 1;
        if(n > 0)
        {
           int end = (n > 10)? 10 : n;
           for(int i = 0; i < end; i++)
           {
               sum += 9 * permutation(9, i);
           }
        }
        return sum;        
    }
        int permutation(int n, int r)
    {
        if(r == 0)
        {
            return 1;
        }else{
            return n * permutation(n - 1, r - 1);
        }
    }
};

2. Count Numbers with Unique Digits Leetcode Solution Java

class Solution {
	public int countNumbersWithUniqueDigits(int n) {
		if (n > 10) {
			return countNumbersWithUniqueDigits(10);
		}
		int count = 1; // x == 0
		long max = (long) Math.pow(10, n);
		boolean[] used = new boolean[10];
		for (int i = 1; i < 10; i++) {
			used[i] = true;
			count += search(i, max, used);
			used[i] = false;
		}
		return count;
	}
	private int search(long prev, long max, boolean[] used) {
		int count = 0;
		if (prev < max) {
			count += 1;
		} else {
			return count;
		}
		for (int i = 0; i < 10; i++) {
			if (!used[i]) {
				used[i] = true;
				long cur = 10 * prev + i;
				count += search(cur, max, used);
				used[i] = false;
			}
		}
		return count;
	}
}

3. Count Numbers with Unique Digits Solution JavaScript

var countNumbersWithUniqueDigits = function(n) {
    return [1,10,91,739,5275,32491,168571,712891,2345851][n]
};

4. Count Numbers with Unique Digits Solution Python

class Solution(object):
    def countNumbersWithUniqueDigits(self, n):
        def count(k):
            if k == max(10 - n, 0):
                return 0
            return k*(1 + count(k - 1))
        if n == 0:
            return 1
        return 9*count(9) + 10