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

31 May, 2020
Prerequisite: map lower_bound() function in C++ STL, map upper_bound() function in C++ STL
In this article, we will discuss the implementation of the lower_bound() and upper_bound() in the Map 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 Map of Pairs lower_bound() for pair(x, y) will return an iterator pointing to the pair whose 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 which points to the pair {Map.size(), 0}.Syntax:mp.lower_bound({a, b})

where,
mp is the map of pairs
and {a, b} whose lower_bound
is to be found

Syntax:
mp.lower_bound({a, b})

where,
mp is the map of pairs
and {a, b} whose lower_bound
is to be found

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 Map of Pairs upper_bound() for pair(x, y) will return an iterator pointing to the pair whose 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 which points to the pair {Map.size(), 0}.Syntax:mp.upper_bound({a, b})

where,
mp is the map of pairs
and {a, b} whose upper_bound
is to be found

Syntax:
mp.upper_bound({a, b})

where,
mp is the map of pairs
and {a, b} whose upper_bound
is to be found

Below is the program to demonstrate lower_bound() and upper_bound() in Map of pairs:
Program 1:
// C++ program to demonstrate lower_bound()// and upper_bound() in Map of Pairs  #include <bits/stdc++.h>using namespace std;  // Function to implement lower_bound()void findLowerBound(    map<pair<int, int>, int>& mp,    pair<int, int>& p){      // This iterator points to the    // lower_bound() of given pair    auto low = mp.lower_bound(p);      cout << "lower_bound() for {2, 5}"         << " is: {"         << (*low).first.first << ", "         << (*low).first.second         << "}" << endl;}  // Function to implement upper_bound()void findUpperBound(    map<pair<int, int>, int>& mp,    pair<int, int>& p){      // This iterator points to the    // upper_bound() of given pair    auto up = mp.upper_bound(p);      cout << "upper_bound() for {2, 5}"         << " is: {"         << (*up).first.first << ", "         << (*up).first.second         << "}" << endl;}  // Driver Codeint main(){    // Declare map of Pairs    map<pair<int, int>, int> mp;      // Insert Pairs in Map    mp.insert({ { 2, 3 }, 8 });    mp.insert({ { 4, 1 }, 5 });    mp.insert({ { 7, 1 }, 3 });    mp.insert({ { 9, 3 }, 1 });    mp.insert({ { 5, 0 }, 3 });      // Given pair {2, 5}    pair<int, int> p = { 2, 5 };      // Function Call to find lower_bound    // of pair p in map mp    findLowerBound(mp, p);      // Function Call to find upper_bound    // of pair p in map mp    findUpperBound(mp, p);      return 0;}
lower_bound() for {2, 5} is: {4, 1}
upper_bound() for {2, 5} is: {4, 1}

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