adding leetcode problems

lectures/08_vector_implementation/README.md

@@ -223,3 +223,8 @@ The destructor is called implicitly when an automatically-allocated object goes
 
 - Finish the definition of Vec::push_back.
 - Write the Vec::resize function.
+
+## 8.16 Leetcode Exercises
+
+- [Leetcode problem 27: Remove Element](https://leetcode.com/problems/remove-element/). Solution: [p27_removeelement.cpp](../../leetcode/p27_removeelement.cpp)
+- [Leetcode problem 263: Ugly Number](https://leetcode.com/problems/ugly-number/). Solution: [p263_uglynumber.cpp](../../leetcode/p263_uglynumber.cpp)

leetcode/p263_uglynumber.cpp

@@ -0,0 +1,24 @@
+class Solution {
+public:
+    // use a non-type parameter as the template parameter list.
+    template <int F>    // F represents factor, and it has to be constant
+    // reduce factor n, has to be reference, because we want to change n.
+    void reduceFactor(int& n){
+        while(n%F==0){
+            n = n/F;
+        }
+    }
+    bool isUgly(int n) {
+        // ugly number has to be a positive integer.
+        if(n<=0){
+            return false;
+        }
+        // reduce factor 2
+        reduceFactor<2>(n);
+        // reduce factor 3
+        reduceFactor<3>(n);
+        // reduce factor 5
+        reduceFactor<5>(n);
+        return (n==1);
+    }
+};

leetcode/p27_removeelement.cpp

@@ -0,0 +1,17 @@
+// note: using template here is completely unnecessary. this is just a demonstration of how to define a templated function.
+
+class Solution {
+public:
+    template <typename T>
+    T removeElement(vector<T>& nums, T val) {
+        int size = nums.size();
+        int j = 0;
+        for(int i=0;i<size;i++){
+            if(nums[i] != val){
+                nums[j] = nums[i];
+                j++;
+            }
+        }
+        return j;
+    }
+};