Java [Leetcode 357]Count Numbers with Unique Digits
2016-08-03 00:03
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题目描述:
Given a non-negative integer n, count all numbers with unique digits, x, where 0 ≤ x < 10n.
Example:
Given n = 2, return 91. (The answer should be the total numbers in the range of 0 ≤ x < 100, excluding
解题思路:
This problem can also be solved using a dynamic programming approach and some knowledge of combinatorics.
Let f(k) = count of numbers with unique digits with length equals k.
f(1) = 10, ..., f(k) = 9 * 9 * 8 * ... (9 - k + 2) [The first factor is 9 because a number cannot start with 0].
代码如下:
Given a non-negative integer n, count all numbers with unique digits, x, where 0 ≤ x < 10n.
Example:
Given n = 2, return 91. (The answer should be the total numbers in the range of 0 ≤ x < 100, excluding
[11,22,33,44,55,66,77,88,99])
解题思路:
This problem can also be solved using a dynamic programming approach and some knowledge of combinatorics.
Let f(k) = count of numbers with unique digits with length equals k.
f(1) = 10, ..., f(k) = 9 * 9 * 8 * ... (9 - k + 2) [The first factor is 9 because a number cannot start with 0].
代码如下:
public class Solution { public int countNumbersWithUniqueDigits(int n) { if(n == 0) return 1; int temp = 9; int res = 0; for(int i = 2; i <= n; i++){ temp *= (9 - i + 2); res += temp; } return res + 10; } }
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