Binary search in sorted vector of pairs
How to apply STL binary_search to vector of pairs(key, value), given that vector is sorted by its first value(key)
struct compare in the code contains two functions which compares the key(searching element) with the first element in the vector
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/* C++ code to demonstrate how Binary Search can be applied on a vector of pairs */#include <bits/stdc++.h>using namespace std; struct compare { bool operator()(const pair<int, int>& value, const int& key) { return (value.first < key); } bool operator()(const int& key, const pair<int, int>& value) { return (key < value.first); }}; int main(){ // initializing the vector of pairs vector<pair<int, int> > vect; // insertion of pairs (key, value) in vector vect vect.push_back(make_pair(1, 20)); vect.push_back(make_pair(3, 42)); vect.push_back(make_pair(4, 36)); vect.push_back(make_pair(2, 80)); vect.push_back(make_pair(7, 50)); vect.push_back(make_pair(9, 20)); vect.push_back(make_pair(3, 29)); // sorting the vector according to key sort(vect.begin(), vect.end()); // printing the sorted vector cout << "KEY" << '\t' << "ELEMENT" << endl; for (pair<int, int>& x : vect) cout << x.first << '\t' << x.second << endl; // searching for the key element 3 cout << "search for key 3 in vector" << endl; if (binary_search(vect.begin(), vect.end(), 3, compare())) cout << "Element found"; else cout << "Element not found"; return 0;} |
KEY ELEMENT 1 20 2 80 3 29 3 42 4 36 7 50 9 20 search for key 3 in vector Element found
The above binary_search operation has time complexity O(lg n)
