Implementation of lower_bound() and upper_bound() in Array of Pairs in C++

Last Updated : 01 Aug, 2020

In this article we will discuss the implementation of the lower_bound() and upper_bound() in an array of pairs.

lower_bound(): It returns an iterator pointing to the first element in the range [first, last) which has a value greater than or equals to the given value “val”. But in Array of Pairs lower_bound() for pair(x, y) will return an iterator pointing to the position of pair whose the first value is greater than or equals x and second value is greater than equals to y.
If the above-mentioned criteria are not met, then it returns an iterator to the index which out of the array of pairs.
upper_bound(): It returns an iterator pointing to the first element in the range [first, last) which has a value greater than the given value “val”. But in Array of Pairs upper_bound() for pair(x, y) will return an iterator pointing to the position of pair whose the first value is greater than x and second value is greater than y.
If the above-mentioned criteria are not met, then it returns an iterator to the index which out of the array of pairs.

Syntax:

// For lower bound
lower_bound(array_name, array_name + array_size, value, comparator_function);

// For upper bound
upper_bound(array_name, array_name + array_size, value, comparator_function);

Parameters: The function lower_bound() and upper_bound() in array of pairs accepts the following parameters:

array_name & array_size: The name and size of the array which represents the interval between [start, end).
value: Value of the lower_bound()/upper_bound() to be searched in the range.
comparator_function: Binary function that accepts two arguments as its input, namely an element of type pair from the array, and the second is the value for which lower_bound()/upper_bound() has to be found and returns a boolean value.

Return Type: It returns an iterator pointing to the first element of the array whose first parameter is greater than or equal to the value.

Below is the program to demonstrate lower_bound() and upper_bound() in array of pairs:

C++

   // C++ program to demonstrate lower_bound() 
// and upper_bound() in Array of Pairs 
#include <bits/stdc++.h> 
using namespace std; 
  
// Function to implement lower_bound() 
void findLowerBound(pair<int, int> arr[], 
                    pair<int, int>& p, 
                    int n) 
{ 
    // Given iterator points to the 
    // lower_bound() of given pair 
    auto low = lower_bound(arr, arr + n, p); 
  
    cout << "lower_bound() for {2, 5}"
         << " is at index: "
         << low - arr << endl; 
} 
  
// Function to implement upper_bound() 
void findUpperBound(pair<int, int> arr[], 
                    pair<int, int>& p, 
                    int n) 
{ 
    // Given iterator points to the 
    // lower_bound() of given pair 
    auto up = upper_bound(arr, arr + n, p); 
  
    cout << "upper_bound() for {2, 5}"
         << " is at index: "
         << up - arr << endl; 
} 
  
// Driver Code 
int main() 
{ 
    // Given sorted array of Pairs 
    pair<int, int> arr[] 
        = { { 1, 3 }, { 1, 7 }, { 2, 4 }, 
            { 2, 5 }, { 3, 8 }, { 8, 6 } }; 
  
    // Given pair {2, 5} 
    pair<int, int> p = { 2, 5 }; 
  
    // Size of array 
    int n = sizeof(arr) / sizeof(arr[0]); 
  
    // Function Call to find lower_bound 
    // of pair p in arr 
    findLowerBound(arr, p, n); 
  
    // Function Call to find upper_bound 
    // of pair p in arr 
    findUpperBound(arr, p, n); 
    return 0; 
} 
 
  

Output:

  lower_bound() for {2, 5} is at index: 3  upper_bound() for {2, 5} is at index: 4

Implementation of lower_bound() and upper_bound() on Map of Pairs in C++

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Implementation of lower_bound() and upper_bound() in Array of Pairs in C++

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