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Python Program to Find closest number in array

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  • Difficulty Level : Medium
  • Last Updated : 27 Jul, 2022

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.  

Python3




# Python3 program to find element
# closest to given target.
 
# Returns element closest to target in arr[]
def findClosest(arr, n, target):
 
    # Corner cases
    if (target <= arr[0]):
        return arr[0]
    if (target >= arr[n - 1]):
        return arr[n - 1]
 
    # Doing binary search
    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 and 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 and target < arr[mid + 1]):
                return getClosest(arr[mid], arr[mid + 1], target)
                 
            # update i
            i = mid + 1
         
    # 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.
def getClosest(val1, val2, target):
 
    if (target - val1 >= val2 - target):
        return val2
    else:
        return val1
 
# Driver code
arr = [1, 2, 4, 5, 6, 6, 8, 9]
n = len(arr)
target = 11
print(findClosest(arr, n, target))
 
# This code is contributed by Smitha Dinesh Semwal


Output: 

9

Time Complexity: O(log(n))

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

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


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