Create Maximum sum subarray of size k.cpp

DSA/Basic-DSA-Questions/Sliding Window/Maximum sum subarray of size k.cpp

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+// This is the code for finding maximum sum of a subarray of size k using sliding
+// window approach. Time complexity: O(n)
+
+#include<bits/stdc++.h>
+using namespace std;
+#define fast              ios::sync_with_stdio(false);cin.tie(0);
+
+int findmaxsum(vector<int>& arr, int k)
+{
+    int sum=0, maxsum=INT_MIN;
+    int i=0, j=0;
+    int n= arr.size();
+
+    while(j<n)
+    {
+        sum+= arr[j];  //add element to sum
+
+        if(j-i+1 <k)   //check if window size reached
+        {
+            j++;
+        }
+        else if((j-i+1)==k)
+        {
+            maxsum= max(maxsum, sum);
+            sum-=arr[i];
+            i++;
+            j++;
+        }
+    }
+    return maxsum;
+}
+
+int main()
+{
+    fast
+    vector<int> arr{1, 4, 2, 10, 23, 3, 1, 0, 20};
+    int k=4;
+    // output will be 39
+
+    cout<<"maximum sum of a subarray of size "<<k<<" is "<< findmaxsum(arr, k);
+
+    return 0;
+}