# 对排序向量中的二分搜索 > 原文： [https://www.geeksforgeeks.org/binary-search-sorted-vector-pairs/](https://www.geeksforgeeks.org/binary-search-sorted-vector-pairs/) 给定向量按其第一个值（关键字）排序的情况下，如何将 [STL binary_search](https://www.geeksforgeeks.org/binary-search-algorithms-the-c-standard-template-library-stl/) 应用于对（关键字，值）的[向量](https://www.geeksforgeeks.org/vector-in-cpp-stl/) 代码中的**结构比较**包含两个函数，将键（搜索元素）与向量中的第一个元素进行比较 ``` /* 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; } ``` **输出**： ``` KEY ELEMENT 1 20 2 80 3 29 3 42 4 36 7 50 9 20 search for key 3 in vector Element found ``` 上面的 binary_search 操作具有时间复杂度 **O（lg n）** * * * * * *