Merge branch 'master' of https://github.com/phumipatc/Algorithm

Author: phumipatc

Divide_and_Conquer/Merge_Sort.cpp

@@ -1,50 +0,0 @@
-/*
-	Task	: Mod_of_Power
-	Author	: Phumipat C. [MAGCARI]
-	School	: RYW
-	Language: C++
-	Explanation Link : https://www.geeksforgeeks.org/multiply-two-polynomials-2/
-	Created	: 03 May 2021 [15:15]
-*/
-
-
-#include<bits/stdc++.h>
-#define all(x) begin(x),end(x)
-#define sz(x) (int)(x).size()
-#define MOD (LL )(1e9+7)
-using namespace std;
-using LL = long long;
-using PII = pair<int ,int >;
-using PLL = pair<long long ,long long >;
-const int dir4[2][4] = {{1,-1,0,0},{0,0,1,-1}};
-const int dir8[2][8] = {{-1,-1,-1,0,1,1,1,0},{-1,0,1,1,-1,0,1,-1}};
-
-
-
-int *multiply(int A[], int B[], int m, int n)
-{
-   int *prod = new int[m+n-1];
-  
-   for (int i = 0; i<m+n-1; i++)
-     prod[i] = 0;
-
-   for (int i=0; i<m; i++)
-   {
-     for (int j=0; j<n; j++)
-         prod[i+j] += A[i]*B[j];
-   }
-  
-   return prod;
-}
-
-void printPoly(int poly[], int n)
-{
-    for (int i=0; i<n; i++)
-    {
-       cout << poly[i];
-       if (i != 0)
-        cout << "x^" << i ;
-       if (i != n-1)
-       cout << " + ";
-    }
-}

Divide_and_Conquer/multiply_two_polynomials.cpp

@@ -0,0 +1,74 @@
+#include<bits/stdc++.h>
+using namespace std;
+
+// put sum of subarrays of size sqrt(n) into block array
+void preprocess_blocks(vector<int>&arr, vector<int>& block)
+{
+    int len=block.size();
+    
+    for(int i=0;i<arr.size();i++)
+    {
+        block[i/len]+=arr[i];
+    }
+    
+}
+
+int main()
+{
+    int n;
+    //input size of array
+    cin>>n;
+    
+    vector<int> arr(n);
+    
+    //input array
+    for(int i=0;i<n;i++)
+        cin>>arr[i];
+    
+    //initialize size of blocks to be sqrt(n)+1
+    int len= sqrt(n)+1;  
+    vector<int> block( len );
+    
+    // preprocess blocks with sum
+    preprocess_blocks(arr, block);    
+    
+    int querySize;
+    //input total queries
+    cin>>querySize;
+    
+    int l,r;
+    //input all the queries
+    while(querySize--)
+    {
+        //1 indexed
+        cin>>l>>r;
+        l--;
+        r--;
+        
+        int sum=0;
+        //traversing l to r efficiently by taking 
+        //already calculated sum from block array
+        for(int i=l;i<=r;)
+        {   
+            //if i is the starting index of a block and that block is in 
+            //the range l to r then take precalculated sum
+            //else take arr[i] to sum
+            if(i%len==0 && i+len-1<=r)
+            {
+                sum+= block[i/len];
+                i+=len;
+            }
+            else
+            {
+                sum+=arr[i];
+                i++;
+            }
+        }
+        
+        //output sum
+        cout<<sum<<endl;
+        
+    }
+    
+    return 0;
+}