leetcode 357. Count Numbers with Unique Digits 解题报告
2016-06-25 20:08
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原题链接
解题思路
很简单找出通项公式,递推求解。解题代码
public class Solution { public int countNumbersWithUniqueDigits(int n) { if(n==0) return 1; if(n==1) return 10; int ans=10;int num = 9;int t=9; for(int i = 1;i< n;i++){ t*=num; num--; ans+=t; } return ans; } }
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