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:
// 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;
} |
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)