Finding Floor and Ceil of a Sorted Array using C++ STL
Given a sorted array, the task is to find the floor and ceil of given numbers using STL.
Examples:
Input: arr[] = {1, 2, 4, 7, 11, 12, 23, 30, 32}, values[] = { 1, 3, 5, 7, 20, 24 } Output: Floor Values: 1 2 4 7 12 23 Ceil values: 1 4 7 7 23 30
In case of floor(): lower_bound() method os STL will be used to find the lower bound. This returns an iterator pointing to the first element in the range [first,last) which does not compare less than the target.
In case of ceil(): upper_bound() method os STL will be used to find the upper bound. This method returns an iterator pointing to the first element in the range [first,last) which compares greater than a target.
Implementation:
CPP
// C++ program to find the floor and ceil // of a given numbers in a sorted array #include <bits/stdc++.h> using namespace std; // Function to find floor of list of // values using lower_bound in STL void printFloor( int arr[], int n1, int findFloor[], int n2) { // Find and print the Floor Values int low; cout << "Floor : " ; for ( int i = 0; i < n2; i++) { low = (lower_bound(arr, arr + n1, findFloor[i]) - arr); if (arr[low] > findFloor[i]) cout << arr[low - 1] << " " ; else cout << arr[low] << " " ; } cout << endl; } ceil // Function to find Ceil of list of // values using upper_bound in STL void printCeil( int arr[], int n1, int findCeil[], int n2) { // Find and print the Ceil Values int up; cout << "Ceil : " ; for ( int i = 0; i < n2; i++) { up = (upper_bound(arr, arr + n1, findCeil[i]) - arr); if (arr[up] > findCeil[i] && arr[up - 1] == findCeil[i]) { cout << arr[up - 1] << " " ; } else cout << arr[up] << " " ; } cout << endl; } // Driver code int main() { // Get the sorted array int arr[] = { 1, 2, 4, 7, 11, 12, 23, 30, 32 }; int n1 = sizeof (arr) / sizeof (arr[0]); // Print Array cout << "Original Array: " ; for (unsigned int i = 0; i < n1; i++) cout << " " << arr[i]; cout << "\n" ; // Given values whose floor and ceil // values are needed to find int find[] = { 1, 3, 5, 7, 20, 24 }; int n2 = sizeof (find) / sizeof (find[0]); // Print Values whose floor // and ceil is to be found cout << "Values: " ; for (unsigned int i = 0; i < n2; i++) cout << find[i] << " " ; cout << "\n" ; // Print Floor Values printFloor(arr, n1, find, n2); // Print Ceil Values printCeil(arr, n1, find, n2); return 0; } |
Output:
Array: 1 2 4 7 11 12 23 30 32 Values: 1 3 5 7 20 24 Floor : 1 2 4 7 12 23 Ceil : 1 4 7 7 23 30
Time Complexity: O(n2*log(n1)+n1)
Auxiliary Space: O(1)