Software Engineering

How to Search a Binary Tree in Java

The challenge

Given a sorted (in ascending order) integer array nums of n elements and a target value, write a function to search target in nums. If target exists, then return its index, otherwise return -1.

Example 1:

Input: nums = [-1,0,3,5,9,12], target = 9
Output: 4
Explanation: 9 exists in nums and its index is 4

Example 2:

Input: nums = [-1,0,3,5,9,12], target = 2
Output: -1
Explanation: 2 does not exist in nums so return -1


  1. You may assume that all elements in nums are unique.
  2. n will be in the range [1, 10000].
  3. The value of each element in nums will be in the range [-9999, 9999].

The solution in Java code

We call the search() method which recursively calls the binarySearch() method for each level.

If we find the target, then we pass back the layer as an integer.

class Solution {
    private int[] nums;
    private int target;
    public int search(int[] nums, int target) {
        this.nums = nums; = target;
        return binarySearch(0, this.nums.length-1);
    private int binarySearch(int start, int end) {
        if (start>end) return -1;
        int m = start+end;
        if ([m]) return m;
        else if (<nums[m]) return binarySearch(start, m-1);
        else return binarySearch(m+1, end);