Count Numbers with Unique Digits

最后要加上countNumbersWithUniqueDigits(n-1)

class Solution {public:    int countNumbersWithUniqueDigits(int n) {        if(n==0)        return 1;        if(n==1)        return 10;                int sum = 9;        int index=9;        int cnt = 0;        while(cnt<n-1){                        sum=sum*index;            cnt++;            index--;        }        return sum+countNumbersWithUniqueDigits(n-1);    }};