refactor 357

fishercoder1534 · fishercoder1534 · commit 1d7ab48a5d61 · 2020-06-10T11:53:08.000-07:00
diff --git a/src/main/java/com/fishercoder/solutions/_357.java b/src/main/java/com/fishercoder/solutions/_357.java
@@ -1,22 +1,5 @@
 package com.fishercoder.solutions;
 
-/**
- * 357. Count Numbers with Unique Digits
- * 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])
-
- Hint:
- A direct way is to use the backtracking approach.
- Backtracking should contains three states which are
- (the current number, number of steps to get that number and a bitmask which
- represent which number is marked as visited so far in the current number).
- Start with state (0,0,0) and count all valid number till we reach number of steps equals to 10n.
- 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].
- */
 public class _357 {
 
     public static class Solution1 {
