LeetCode – Count Numbers with Unique Digits (Java)

Given a non-negative integer n, count all numbers with unique digits, x, where x is from 0 to 10^n-1.

Java Solution

public int countNumbersWithUniqueDigits(int n) {
    int[] arr = new int[n+1];
    arr[0]=1; // x can be 0
 
    for(int i=1; i<=n; i++){
        arr[i]=9;
        for(int j=9; j>=9-i+2; j--){
            arr[i] *= j;
        }
    }
 
    int result =0;
    for(int i: arr)
        result += i;
 
    return result;
}
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