adding exercise on map find function

lectures/15_maps_I/README.md

@@ -165,5 +165,6 @@ on whether or not the key was in a pair in the map.
 ## 15.10 Leetcode Exercises
 
 - [Leetcode problem 1: Two Sum](https://leetcode.com/problems/two-sum/). Solution: [p1_twosum.cpp](../../leetcode/p1_twosum.cpp).
+- [Leetcode problem 219: Contains Duplicate II](https://leetcode.com/problems/contains-duplicate-ii/description/). Solution: [p219_contains_duplicate_ii.cpp](../../leetcode/p219_contains_duplicate.cpp).
 - [Leetcode problem 290: Word Pattern](https://leetcode.com/problems/word-pattern/). Solution: [p290_word_pattern.cpp](../../leetcode/p290_word_pattern.cpp).
 

leetcode/p219_contains_duplicate_ii.cpp

@@ -0,0 +1,18 @@
+class Solution {
+public:
+    bool containsNearbyDuplicate(vector<int>& nums, int k) {
+        int size = nums.size();
+        // create the map, map key is the value of the vector element, map value is the index of that element in the vector.
+        map<int,int> map1;
+        for(int i=0;i<size;i++){
+            // if already exists
+            if(map1.find(nums[i])!=map1.end()){
+                if(i-map1[nums[i]]<=k){
+                    return true;
+                }
+            }
+            map1[nums[i]]=i;
+        }
+        return false;
+    }
+};