6. Maximum Length of Repeated Subarray (HASHING)

Author: akash-rajak

Hashing/C++/6. Maximum Length of Repeated Subarray (HASHING).cpp

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+
+// Maximum Length of Repeated Subarray
+
+/*
+
+Question : We will be given two array A and B of any size, and we need to compute the Maximum length of subarray which is present in both.
+
+Algorithm :
+	We will use hashing algorithm to solve this problem.
+	First will make a hash table for array A, to store the index of each element of A.
+	Then for each element of array B, will loop through the size of the hash value of that array B element and update the ans accordingly
+
+*/
+
+
+#include<bits/stdc++.h>
+using namespace std;
+
+int max_length_of_repeated_subarray(int a[ ], int b[ ], int n, int m) 
+{
+	// ans variable defined to store the answer of max length and initialized to 0
+    int ans = 0;
+    // unordered map taken for storing hash value of array a
+    unordered_map<int, vector<int>> hash_a;
+    for (int i=0;i<n;i++) 
+	{
+        hash_a[a[i]].push_back(i); // stored indices of each array element in hashtable
+    }
+    
+    // Now we loop through all the element of array b
+    for (int i=0;i<m;i++) 
+	{
+		// and for each element of B, we loop through the value of size of hash value for that value 
+        for (int j = 0; j < hash_a[b[i]].size(); j++) 
+		{
+            int k = 0;
+            // for each of i and j we check the condition for maximum subarray length
+            while (i+k<m && hash_a[b[i]][j] + k<n && b[i+k]==a[hash_a[b[i]][j]+k]) 
+			{
+				k++;// and if satisfies will keep on updating the values of k
+			}
+			// updating the ans if k we got is greater than previous ans
+            if(k>ans)
+            ans = k;
+        }
+    }
+    return ans;//returning the final answer
+}
+
+int main()
+{
+	// declared two variable n and m, for size of both array
+	int n,m;
+	// taking input of both array size
+	cin>>n>>m;
+	// declared two array a and b of size n and m respectively.
+	int a[n], b[m];
+	// taking input of the element in array a
+	for(int i=0;i<n;i++)
+	{
+		cin>>a[i];
+	}
+	// taking input of the element in array b
+	for(int i=0;i<m;i++)
+	{
+		cin>>b[i];
+	}
+	
+	// function called for finding the maximum lenght of repeated subarray
+	cout<<"The Maximum length of repeated subarray is  :  "<<max_length_of_repeated_subarray(a,b,n,m)<<endl;
+	
+	return 0;
+}
+
+/*
+
+Time Complexity : O(n*m*k)
+Space Complexity : O(n)
+
+Sample testcase :
+Input 1 :
+	5
+	5
+	10 23 17 2 3
+	23 17 4 5 19
+Output 1:
+	The Maximum length of repeated subarray is  :  2
+	
+Input 2 :
+	5
+	4
+	7 3 5 6 1
+	3 2 4 5
+Output 1:
+	The Maximum length of repeated subarray is  :  1
+
+*/
+