readme update

Author: EISAWESOME

README.md

@@ -176,4 +176,34 @@ Hint: Try preprocessing the dictionary into a more efficient data structure to s
 ### Solution
 [JS](pb11/answer.js) (1:28)
 
-[Python](pb11/answer.py)
+[Python](pb11/answer.py)
+
+---
+
+## 12
+> This problem was asked by Amazon.
+
+There exists a staircase with N steps, and you can climb up either 1 or 2 steps at a time. Given N, write a function that returns the number of unique ways you can climb the staircase. The order of the steps matters.
+For example, if N is 4, then there are 5 unique ways:
+```
+1, 1, 1, 1
+2, 1, 1
+1, 2, 1
+1, 1, 2
+2, 2
+```
+What if, instead of being able to climb 1 or 2 steps at a time, you could climb any number from a set of positive integers X? For example, if `X = {1, 3, 5}`, you could climb 1, 3, or 5 steps at a time.
+
+### Solution
+[JS](pb12/answer.js) (Partial solution only)
+
+---
+
+## 13
+> This problem was asked by Amazon.
+
+Given an integer k and a string s, find the length of the longest substring that contains at most k distinct characters.
+For example, given s = "abcba" and k = 2, the longest substring with k distinct characters is "bcb".
+
+### Solution
+[JS](pb13/answer.js) (10:47)