segment tree to find sum in a particular interval of an array and to update the value at a particular index of the array.

SegmentTree.java

/*package whatever //do not write package name here */
import java.lang.Math;
public class segmentTree
{
    static int a[] = {1,2,3,4,5};
    static int tree[];  //segment tree that you will construct
    
    public static void buildTree(int sb,int se)
    {
        int numOfLeaves=a.length;
        int height = (int)(Math.ceil(Math.log(numOfLeaves)/Math.log(2))); //not really used
        int totalNodes = 2*numOfLeaves - 1; //total = n leaves(values in array a) + n-1 internal nodes in a"full" binary tree 
        tree = new int[totalNodes];     //above statement is always true .
        buildTreeFinal(sb, se,0);   //tree will have exactly "totalNodes" no. of nodes.
        
    }
    
    public static void getSum(int sb,int se)  //s = segment b=beginning e = end
    {
        if((sb<0 || sb > a.length-1)||(se<0 || se > a.length - 1) ||(se<sb))
        {
            System.out.println("Invalid input");
            System.exit(0);
        }
        System.out.println(getSumFinal(0,a.length-1,sb,se,0));
    }
    
    public static int getSumFinal(int sb,int se,int b,int e,int ci) //ci = current index in the segment array
    {
        if(sb >= b && se <= e)
        return tree[ci];
        
        if(sb > e || se < b)
        return 0;
        
        int m=sb+(se-sb)/2;
        return(getSumFinal(sb,m,b,e,2*ci+1)+getSumFinal(m+1,se,b,e,2*ci+2));
    }
    
    public static void update(int val,int i) //update at index i. array a is untoched.
    {
        updateFinal(val,i,0,a.length-1,0);
    }
    public static int updateFinal(int val,int i,int sb,int se,int ci)
    {
        if(sb==se)
        {
            int tmp=tree[ci];
            tree[ci]=val;
            return tmp;
        }
        int x,y;
        int m = sb+(se-sb)/2;
        if(i <= m)
        {
        y = updateFinal(val,i,sb,m,2*ci+1);
        x = 2*ci+1;
        }
        else
        {
         y = updateFinal(val,i,m+1,se,2*ci+2);
         x = 2*ci+2;
        }
        
        tree[x] = tree[x] - y + val;
        return y;
    }
    
    public static int buildTreeFinal(int sb,int se,int ci)
    {
        if(sb==se)
        {
            tree[ci]=a[sb];
            return a[sb];
        }
        
        int mid=sb+(se-sb)/2;
        tree[ci]=buildTreeFinal(sb,mid,2*ci+1)+buildTreeFinal(mid+1,se,2*ci+2);
        return tree[ci];
        
    }
    
    public static void main(String args[])
    {

       buildTree(0,a.length-1);  //a is the original array 
       getSum(4,4);
       update(5,0);
       getSum(0,1);
       update(5,1);
       getSum(0,2);

    }
}