Find floor and ceil in an unsorted array

Given an unsorted array arr[] and an element x, find floor and ceiling of x in arr[0..n-1].

Floor of x is the largest element which is smaller than or equal to x. Floor of x doesn’t exist if x is smaller than smallest element of arr[].

Ceil of x is the smallest element which is greater than or equal to x. Ceil of x doesn’t exist if x is greater than greates element of arr[].

Examples:

Input : arr[] = {5, 6, 8, 9, 6, 5, 5, 6}      
        x = 7
Output : Floor = 6
         Ceiling = 8

Input : arr[] = {5, 6, 8, 9, 6, 5, 5, 6}      
        x = 6
Output : Floor = 6
         Ceiling = 6

Input : arr[] = {5, 6, 8, 9, 6, 5, 5, 6}      
        x = 10
Output : Floor = 9
         Ceiling doesn't exist.

Recommended: Please solve it on “PRACTICE ” first, before moving on to the solution.

Method 1 (Use Sorting)
1) Sort input array.
2) Use binary search to find floor and ceiling of x. Refer this and this for implementation of floor and ceiling in a sorted array.

Time Complexity : O(n log n)
Auxiliary Space : O(1)

This solution is works well if there are multiple queries of floor and ceiling on a static array. We can sort the array once and answer the queries in O(Log n) time.

Method 2 (Use Linear Search
The idea is to traverse array and keep track of two distances with respect to x.
1) Minimum distance of element greater than or equal to x.
2) Minimum distance of element smaller than or equal to x.
Finally print elements with minimum distances.

C/C++

// C++ program to find floor and ceiling in an 
// unsorted array. 
#include<bits/stdc++.h> 
using namespace std; 
  
// Function to floor and ceiling of x in arr[] 
void floorAndCeil(int arr[], int n, int x) 
{ 
    // Indexes of floor and ceiling 
    int fInd, cInd; 
  
    // Distances of current floor and ceiling 
    int fDist = INT_MAX, cDist = INT_MAX; 
  
    for (int i=0; i<n; i++) 
    { 
        // If current element is closer than 
        // previous ceiling. 
        if (arr[i] >= x && cDist > (arr[i] - x)) 
        { 
           cInd = i; 
           cDist = arr[i] - x; 
        } 
  
        // If current element is closer than 
        // previous floor. 
        if (arr[i] <= x && fDist > (x - arr[i])) 
        { 
           fInd = i; 
           fDist = x - arr[i]; 
        } 
    } 
  
    if (fDist == INT_MAX) 
      cout << "Floor doesn't exist " << endl; 
    else
      cout << "Floor is "  << arr[fInd] << endl; 
  
    if (cDist == INT_MAX) 
      cout << "Ceil doesn't exist " << endl; 
    else
      cout << "Ceil is "  << arr[cInd] << endl; 
} 
  
// Driver code 
int main() 
{ 
    int arr[] = {5, 6, 8, 9, 6, 5, 5, 6}; 
    int n = sizeof(arr)/sizeof(int); 
    int x = 7; 
    floorAndCeil(arr, n, x); 
    return 0; 
} 

Java

// Java program to find floor and ceiling in an 
// unsorted array. 
import java.io.*; 
  
class GFG  
{ 
     // Function to floor and ceiling of x in arr[] 
    public static void floorAndCeil(int arr[], int x) 
    { 
        int n = arr.length; 
          
        // Indexes of floor and ceiling 
        int fInd = -1, cInd = -1; 
   
        // Distances of current floor and ceiling 
        int fDist = Integer.MAX_VALUE, cDist = Integer.MAX_VALUE; 
   
        for (int i = 0; i < n; i++) 
        { 
            // If current element is closer than 
            // previous ceiling. 
            if (arr[i] >= x && cDist > (arr[i] - x)) 
            { 
                cInd = i; 
                cDist = arr[i] - x; 
            } 
   
            // If current element is closer than 
            // previous floor. 
            if (arr[i] <= x && fDist > (x - arr[i])) 
            { 
                fInd = i; 
                fDist = x - arr[i]; 
            } 
        } 
   
        if(fDist == Integer.MAX_VALUE) 
            System.out.println("Floor doesn't exist " ); 
        else
            System.out.println("Floor is " +  arr[fInd]); 
   
        if(cDist == Integer.MAX_VALUE) 
            System.out.println("Ceil doesn't exist "); 
        else
            System.out.println("Ceil is  " + arr[cInd]); 
    } 
      
    public static void main (String[] args)  
    { 
        int arr[] = {5, 6, 8, 9, 6, 5, 5, 6}; 
        int x = 7; 
        floorAndCeil(arr, x); 
    } 
} 

Python 3

# Python 3 program to find  
# floor and ceiling in an 
# unsorted array. 
  
import sys 
  
# Function to floor and 
# ceiling of x in arr[] 
def floorAndCeil(arr, n, x): 
  
    # Distances of current 
    # floor and ceiling 
    fDist = sys.maxsize 
    cDist = sys.maxsize 
  
    for i in range(n): 
      
        # If current element is closer  
        # than previous ceiling. 
        if (arr[i] >= x and 
            cDist > (arr[i] - x)): 
          
            cInd = i 
            cDist = arr[i] - x 
  
        # If current element is closer  
        # than previous floor. 
        if (arr[i] <= x and fDist > (x - arr[i])): 
          
            fInd = i 
            fDist = x - arr[i] 
  
    if (fDist == sys.maxsize): 
        print("Floor doesn't exist ") 
    else: 
        print("Floor is " + str(arr[fInd]))  
  
    if (cDist == sys.maxsize): 
        print( "Ceil doesn't exist ") 
    else: 
        print("Ceil is " + str(arr[cInd])) 
  
# Driver code 
if __name__ == "__main__": 
    arr = [5, 6, 8, 9, 6, 5, 5, 6] 
    n = len(arr) 
    x = 7
    floorAndCeil(arr, n, x) 
  
# This code is contributed  
# by ChitraNayal 

C#

// C# program to find floor and ceiling in an 
// unsorted array. 
using System; 
  
class GFG { 
      
    // Function to floor and ceiling of x in arr[] 
    public static void floorAndCeil(int []arr, int x) 
    { 
        int n = arr.Length; 
          
        // Indexes of floor and ceiling 
        int fInd = -1, cInd = -1; 
  
        // Distances of current floor and ceiling 
        int fDist = int.MaxValue, 
            cDist =int.MaxValue; 
              
        for (int i = 0; i < n; i++) 
        { 
              
            // If current element is closer than 
            // previous ceiling. 
            if (arr[i] >= x && cDist > (arr[i] - x)) 
            { 
                cInd = i; 
                cDist = arr[i] - x; 
            } 
  
            // If current element is closer than 
            // previous floor. 
            if (arr[i] <= x && fDist > (x - arr[i])) 
            { 
                fInd = i; 
                fDist = x - arr[i]; 
            } 
        } 
  
        if(fDist == int.MaxValue) 
            Console.Write("Floor doesn't exist " ); 
        else
            Console.WriteLine("Floor is " + arr[fInd]); 
  
        if(cDist == int.MaxValue) 
        Console.Write("Ceil doesn't exist "); 
        else
            Console.Write("Ceil is " + arr[cInd]); 
    } 
      
    // Driver code 
    public static void Main ()  
    { 
        int []arr = {5, 6, 8, 9, 6, 5, 5, 6}; 
        int x = 7; 
          
        floorAndCeil(arr, x); 
    } 
} 
  
// This code is contributed by nitin mittal. 

PHP

<?php 
// PHP program to find  
// floor and ceiling in  
// an unsorted array. 
  
// Function to floor and  
// ceiling of x in arr[] 
function floorAndCeil($arr, 
                      $n, $x) 
{ 
    // Indexes of floor 
    // and ceiling 
    $fInd = 0; 
    $cInd = 0; 
  
    // Distances of current 
    // floor and ceiling 
    $fDist = 999999; 
    $cDist = 999999; 
  
    for ($i = 0; $i < $n; $i++) 
    { 
        // If current element  
        // is closer than 
        // previous ceiling. 
        if ($arr[$i] >= $x &&  
            $cDist > ($arr[$i] - $x)) 
        { 
            $cInd = $i; 
            $cDist = $arr[$i] - $x; 
        } 
  
        // If current element  
        // is closer than 
        // previous floor. 
        if ($arr[$i] <= $x &&  
            $fDist > ($x - $arr[$i])) 
        { 
            $fInd = $i; 
            $fDist = $x - $arr[$i]; 
        } 
    } 
  
    if ($fDist == 999999) 
        echo "Floor doesn't ".  
             "exist " . "\n" ; 
    else
        echo "Floor is " .  
              $arr[$fInd] . "\n"; 
  
    if ($cDist == 999999) 
        echo "Ceil doesn't " . 
             "exist " . "\n"; 
    else
        echo "Ceil is " .  
             $arr[$cInd] . "\n"; 
} 
  
// Driver code 
$arr = array(5, 6, 8, 9, 
             6, 5, 5, 6); 
$n = count($arr); 
$x = 7; 
floorAndCeil($arr, $n, $x); 
  
// This code is contributed 
// by Sam007 
?> 

Output :

Floor is 6
Ceil is 8

Time Complexity : O(n)
Auxiliary Space : O(1)

Related Articles :
Ceiling in a sorted array
Floor in a sorted array

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My Personal Notes

Recommended: Please solve it on “PRACTICE ” first, before moving on to the solution.

C/C++

Java

Python 3

C#

PHP

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