adding leetcode problem

lectures/04_pointers/README.md

@@ -188,6 +188,4 @@ std::sort( a, a+n );
 
 ## 4.10 Exercises
 
-- [Leetcode problem 905: Sort Array By Parity](https://leetcode.com/problems/sort-array-by-parity/). Solution: [p905_sortarraybyparity.cpp](../../leetcode/p905_sortarraybyparity.cpp)
+- [Leetcode problem 26: Remove Duplicates from Sorted Array](https://leetcode.com/problems/remove-duplicates-from-sorted-array/). Solution: [p26_removeduplicates.cpp](../../leetcode/p26_removeduplicates.cpp)
-- [Leetcode problem 977: Squares of a Sorted Array](https://leetcode.com/problems/squares-of-a-sorted-array/). Solution: [p977_sortedsquare.cpp](../../leetcode/p977_sortedsquare.cpp)
-- [Leetcode problem 1051: Height Checker](https://leetcode.com/problems/height-checker/). Solution: [p1051_heightchecker.cpp](../../leetcode/p1051_heightchecker.cpp)

leetcode/p26_removeduplicates.cpp

@@ -0,0 +1,79 @@
+class Solution {
+public:
+    /* // just use vectors
+    int removeDuplicates(vector<int>& nums) {
+        int size = nums.size();
+        if(size == 0){
+            return 0;
+        }
+        if(size == 1){
+            return 1;
+        }
+        // nums has at least 2 elements
+        int j = 1;
+        for(int i=0;i<size-1;i++){
+            if(nums[i+1]!=nums[i]){
+                // meaning nums[i+1] is a new number, we should store it in nums[j]
+                nums[j] = nums[i+1];
+                j++;
+            }
+        }
+        return j;
+    }*/
+
+    /* // use C arrays
+    int removeDuplicates(vector<int>& nums) {
+        int size = nums.size();
+        int array[size];
+        for(int i=0;i<size;i++){
+            array[i] = nums[i];
+        }
+        if(size == 0){
+            return 0;
+        }
+        if(size == 1){
+            return 1;
+        }
+        // nums has at least 2 elements
+        int j = 1;
+        for(int i=0;i<size-1;i++){
+            if(array[i+1]!=array[i]){
+                // meaning nums[i+1] is a new number, we should store it in nums[j]
+                array[j] = array[i+1];
+                j++;
+            }
+        }
+        for(int i=0;i<j;i++){
+            nums[i] = array[i];
+        }
+        return j;
+    }*/
+
+    // use c arrays with pointer arithmetic
+    int removeDuplicates(vector<int>& nums) {
+        int size = nums.size();
+        int array[size];
+        for(int i=0;i<size;i++){
+            *(array+i) = nums[i];
+        }
+        if(size == 0){
+            return 0;
+        }
+        if(size == 1){
+            return 1;
+        }
+        // nums has at least 2 elements
+        int j = 1;
+        for(int i=0;i<size-1;i++){
+            if(*(array+i+1)!=*(array+i)){
+                // meaning nums[i+1] is a new number, we should store it in nums[j]
+                *(array+j) = *(array+i+1);
+                j++;
+            }
+        }
+        for(int i=0;i<j;i++){
+            nums[i] = *(array+i);
+        }
+        return j;
+    }
+};