Java Program to Find closest number in array

Last Updated : 13 Apr, 2023

Given an array of sorted integers. We need to find the closest value to the given number. Array may contain duplicate values and negative numbers.

Examples:

Input : arr[] = {1, 2, 4, 5, 6, 6, 8, 9}
             Target number = 11
Output : 9
9 is closest to 11 in given array

Input :arr[] = {2, 5, 6, 7, 8, 8, 9}; 
       Target number = 4
Output : 5

A simple solution is to traverse through the given array and keep track of absolute difference of current element with every element. Finally return the element that has minimum absolution difference.

An efficient solution is to use Binary Search.

Java

// Java program to find element closest to given target.
import java.util.*;
import java.lang.*;
import java.io.*;

class FindClosestNumber {
    
    // Returns element closest to target in arr[]
    public static int findClosest(int arr[], int target)
    {
        int n = arr.length;

        // Corner cases
        if (target <= arr[0])
            return arr[0];
        if (target >= arr[n - 1])
            return arr[n - 1];

        // Doing binary search 
        int i = 0, j = n, mid = 0;
        while (i < j) {
            mid = (i + j) / 2;

            if (arr[mid] == target)
                return arr[mid];

            /* If target is less than array element,
               then search in left */
            if (target < arr[mid]) {
       
                // If target is greater than previous
                // to mid, return closest of two
                if (mid > 0 && target > arr[mid - 1]) 
                    return getClosest(arr[mid - 1], 
                                  arr[mid], target);
                
                /* Repeat for left half */
                j = mid;              
            }

            // If target is greater than mid
            else {
                if (mid < n-1 && target < arr[mid + 1]) 
                    return getClosest(arr[mid], 
                          arr[mid + 1], target);                
                i = mid + 1; // update i
            }
        }

        // Only single element left after search
        return arr[mid];
    }

    // Method to compare which one is the more close
    // We find the closest by taking the difference
    //  between the target and both values. It assumes
    // that val2 is greater than val1 and target lies
    // between these two.
    public static int getClosest(int val1, int val2, 
                                         int target)
    {
        if (target - val1 >= val2 - target) 
            return val2;        
        else 
            return val1;        
    }

    // Driver code
    public static void main(String[] args)
    {
        int arr[] = { 1, 2, 4, 5, 6, 6, 8, 9 };
        int target = 11;
        System.out.println(findClosest(arr, target));
    }
}

Output:

Time Complexity: O(log(n))
Auxiliary Space: O(log(n)) (implicit stack is created due to recursion)

Approach 2: Using Two Pointers

Another approach to solve this problem is to use two pointers technique, where we maintain two pointers left and right, and move them towards each other based on their absolute difference with target.

Below are the steps:

Initialize left = 0 and right = n-1, where n is the size of the array.
Loop while left < right
1. If the absolute difference between arr[left] and target is less than or equal to the absolute difference between arr[right] and target, move left pointer one step to the right, i.e. left++
2. Else, move right pointer one step to the left, i.e. right–-
Return arr[left], which will be the element closest to the target.

Below is the implementation of the above approach:

Java

// Java program to find element
// closest to given target using two pointers
import java.util.*;

public class GFG {
    public static int findClosest(int[] arr, int n,
                                  int target)
    {
        int left = 0, right = n - 1;
        while (left < right) {
            if (Math.abs(arr[left] - target)
                <= Math.abs(arr[right] - target)) {
                right--;
            }
            else {
                left++;
            }
        }
        return arr[left];
    }

    public static void main(String[] args)
    {
        int[] arr = { 1, 2, 4, 5, 6, 6, 8, 8, 9 };
        int n = arr.length;
        int target = 11;
        System.out.println(findClosest(arr, n, target));
    }
}
// This code is contributed by Susobhan Akhuli

Output

Time Complexity: O(N), where n is the length of the array.
Auxiliary Space: O(1)

Please refer complete article on Find closest number in array for more details!

Java Program to Find closest number in array

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Java Program to Find closest number in array

Approach 2: Using Two Pointers

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