adding cp3

labs/11_hash_tables/README.md

@@ -24,9 +24,38 @@ Finally, implement and test the *resize* function. This function is automaticall
 
 **To complete this checkpoint**: Show a TA these additions and the test output.
 
-## Checkpoint 3
+## Checkpoint 3: Using std::unordered_map
 
-*estimate: remainder of lab time*
+*estimate: 20-30 minutes*
 
-To be added.
+Complete the *isHappy* function in this [program](test_happy_number.cpp). This function determines if a number n is happy or not. You can assume 1<=n<50000. Do not include extra libraries.
 
+A happy number is a number defined by the following process:
+
+- Starting with any positive integer, replace the number by the sum of the squares of its digits.
+- Repeat the process until the number equals 1 (where it will stay), or it loops endlessly in a cycle which does not include 1.
+- Those numbers for which this process ends in 1 are happy.
+
+Return true if n is a happy number, and false if not. Here are some examples:
+
+```console
+Example 1:
+
+Input: n = 19
+Output: true
+
+Explanation:
+12 + 92 = 82
+82 + 22 = 68
+62 + 82 = 100
+12 + 02 + 02 = 1
+```
+
+```console
+Example 2:
+
+Input: n = 2
+Output: false
+```
+
+**To complete this checkpoint**: Show a TA your program and the test results.