357. Count Numbers with Unique Digits

class Solution {
public:
    int countNumbersWithUniqueDigits(int n) {
        int ret=1;
        int product=1;
        for(int i=0,j=9;i 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 static 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;
	}
}
*/

/*
class Solution {
public:
    int countNumbersWithUniqueDigits(int n) {
        vector tbl(min(n,10)+1, 1);
        for (int i = 1; i <= min(n,10); i++)
            tbl[i] = tbl[i-1] * (i == 1? 9: (9-i+2));
        return accumulate(tbl.begin(), tbl.end(), 0);
    }
};
*/