Add C++ solution for 0658-find-k-closest-elements

cpp/0658-find-k-closest-elements.cpp

@@ -0,0 +1,61 @@
+// Approach: Binary Search + Two‑Pointer Window Expansion (More Intuitive)
+// Runtime: 0 ms (100%);  Memory: 35.7 MB (99%)
+// Time Complexity: O(log(n) + k), Space Complexity: O(1)
+
+class Solution {
+public:
+    vector<int> findClosestElements(vector<int>& arr, int k, int x) {
+
+        // Part 1: Binary Sarch to find x or element in arr closest to x
+        int l=0;
+        int r = arr.size()-1;
+        int closestVal = arr[0];
+        int closestIndex = 0;
+
+        while(l<=r){
+            int m = (l+r)/2;
+            int currDiff = abs(arr[m] - x);
+            int resDiff = abs(closestVal - x);
+
+            if((currDiff< resDiff) || (currDiff == resDiff && arr[m]<closestVal)){
+                closestVal = arr[m];
+                closestIndex = m;
+            }
+
+            if (arr[m]<x){
+                l=m+1;
+            }
+            else if(arr[m]>x){
+                r= m-1;
+            }
+            else{
+                break;
+            }
+
+        }
+
+        //Part 2: Binary Search to find the window of k such elements
+        l=closestIndex;
+        r=closestIndex;
+
+        for( int i=0; i<k-1;i++){ 
+            if(l==0){
+                r+=1;
+            }
+            else if(r== arr.size()-1 ){
+                l-=1;
+            }
+            else if (x - arr[l - 1] <= arr[r + 1] - x){
+                l-=1;
+            }
+            else{
+                r+=1;
+
+            }
+
+
+        }
+        return vector<int>(arr.begin() + l, arr.begin() + r + 1);
+
+    }
+};