Segment Tree For Min Query Java

public class SegmentTreeMin {

private static int[] arr = {1,9,2,3,5,8,90,1,2,88};

private static Node[] stArr;

private static int query(int root,int low,int high) {

//System.out.println("query");

if(root>=stArr.length) return -1;

Node n = stArr[root];

//no intesection

if(low > n.r || high < n.l) {

return -1;

}

//n is contained between low & high

if(n.l >= low && n.r <= high) {

return n.val;

}

//low <= n.r && high >= n.l

int l_ind = query(root*2+1,low,high);

int r_ind = query(root*2+2,low,high);

int min = Integer.MAX_VALUE;

int min_index = -1;

if(l_ind > -1) {min = arr[l_ind];min_index = l_ind;}

if(r_ind > -1 && arr[r_ind] < min) {min = arr[r_ind];min_index = r_ind;}

return min_index;

}

private static void construct(int root,int low,int high) {

if(high<low) return;

if(root>=stArr.length) return;

Node n = new Node(low,high);

stArr[root] = n;

if(low==high) { n.val = low; return;}

int mid = low + (high-low)/2;

construct(2*root+1,low,mid);

construct(2*root+2,mid+1,high);

Node left = stArr[2*root+1];

Node right = stArr[2*root+2];

int lval  = left!=null?arr[left.val]:Integer.MAX_VALUE;

int rval  = right!=null?arr[right.val]:Integer.MAX_VALUE;

if(lval<rval) n.val = left.val; else n.val = right.val;

}

public static void main(String[] args) {

int stlen = (int) Math.ceil(Math.log(arr.length*1l)/Math.log(2l)) + 1;

stArr = new Node[(int)( Math.pow(2, stlen) - 1)];

construct(0,0, arr.length-1);

int min_index = query(0,5,7);

int minVal = min_index > -1?arr[min_index]:-1;

System.out.println(minVal);

/*for(int i=0;i<stArr.length;i++) {

Node n = stArr[i];

if(n!=null) {

System.out.println(i+" "+n.l+" "+n.r+" "+n.val);

}

}*/

}

}

class Node {

int l;

int r;

int val;

public Node(int l,int r) {

this.l = l;

this.r = r;

}

}