added segment trees #411

Data Structures/segment-trees/seg.cpp

@@ -0,0 +1,116 @@
+/* 
+  P.Kishore
+  Segment- Tree Implementation 
+          Version 1: Range minimum query with point updates
+*/
+
+#include<bits/stdc++.h>
+using namespace std;
+const int max_size=100005;
+int arr[max_size],seg[4*max_size];
+
+// Initially building the tree with the given array arr
+
+void build(int low,int high,int pos)
+{
+  if(low==high)
+  {
+   seg[pos]=arr[low];
+   return;
+  }
+
+  int mid=(low+high)/2;
+
+  build(low,mid,2*pos+1);
+
+  build(mid+1,high,2*pos+2);
+
+  seg[pos]=min(seg[2*pos+1],seg[2*pos+2]);
+}
+
+
+// Updating some position in array (ie: arr[index]=value)
+
+void update(int low,int high,int pos,int index,int value)
+{
+  if(low==high)
+  {
+    arr[index]=value;
+    seg[pos]=arr[index];
+    return; 
+  }
+
+  int mid=(low+high)/2;
+
+  if(index<=mid)
+  	update(low,mid,2*pos+1,index,value);
+  else
+  	update(mid+1,high,2*pos+2,index,value);
+
+  seg[pos]=min(seg[2*pos+1],seg[2*pos+2]);
+}
+
+
+// QUERY - Returns minimum in the range arr[qlow,qhigh]
+
+int query(int low,int high,int pos,int qlow,int qhigh)
+{
+  if(high<qlow || qhigh<low) // Out of range
+  	return INT_MAX;
+
+  else if(qlow<=low && high<=qhigh) // Completely within range
+  	return seg[pos];
+
+  int mid=(low+high)/2;
+
+  int q1=query(low,mid,2*pos+1,qlow,qhigh);
+  int q2=query(mid+1,high,2*pos+2,qlow,qhigh);
+
+  return min(q1,q2);
+}
+
+int main()
+{
+  cout<<"Enter the number of elements \n";
+  int n;
+  cin>>n;
+  int i;
+
+  for(i=0;i<n;i++)
+  	cin>>arr[i];
+
+  build(0,n-1,0);
+
+  cout<<"Enter the total number of updates and queries\n";
+
+  int m;
+
+  cin>>m;
+
+  cout<<"Enter them in the form\n";
+  cout<<"For Update : 1 index value\n";
+  cout<<"For query  : 2 left right\n";
+
+
+  int type,L,R,index,value;
+
+ for(i=0;i<m;i++)
+ {
+   cin>>type;
+
+   if(type==1)
+   {
+     cin>>index>>value;
+     update(0,n-1,0,index,value);	
+   }
+
+   else
+   {
+   	cin>>L>>R;  
+   	cout<<query(0,n-1,0,L,R)<<endl;
+   }
+
+ }
+
+ return 0;	
+}