C++STLのバイナリ検索関数

二分探索は、ソートされた配列内のターゲット値の位置を見つける検索アルゴリズムです。二分探索は、ターゲット値をソートされた配列の中央の要素と比較します。二分探索の時間計算量はO（1）です。これは、さまざまな実装を行うC++プログラムです。 C++STLのバイナリ検索機能

アルゴリズム

Begin
   Initialize the vector of integer values.
   The functions are used here:
   binary_search(start_pointer, end_pointer, value) = Returns true if the value present in array otherwise    false.

   lower_bound(start_pointer, end_pointer, value) = Returns pointer to “position of value” if container 
      contains 1 occurrence of value. Returns pointer to “first position of value” if container contains 
      multiple occurrence of value. Returns pointer to “position of next higher number than value” if container does not contain occurrence of value.

   upper_bound(start_pointer, end_pointer, value) = Returns pointer to “position of next higher valuethan 
      value” if container contains 1 occurrence of value. Returns pointer to “first position of next higher 
      number than last occurrence of value” if container contains multiple occurrence of value. Returns 
      pointer to “position of next higher number than value” if container does not contain occurrence of value.
   Print the results.
End.

サンプルコード

#include<bits/stdc++.h>
using namespace std;
int main() {
   vector<int> a = {6,7,10,14,16,20};
   if (binary_search(a.begin(), a.end(), 50))
      cout << "50 exists in vector";
   else
      cout << "50 does not exist";
   cout << endl;
   if (binary_search(a.begin(), a.end(), 7))
      cout << "7 exists in the vector";
   else
      cout << "7 does not exist";
   cout << endl;
   cout << "The position of 7 using lower_bound ";
   cout << lower_bound(a.begin(), a.end(), 7) - a.begin();
   cout << endl;
   cout << "The position of 7 using upper_bound ";
   cout << upper_bound(a.begin(), a.end(), 7) - a.begin();
   cout << endl;
}

出力

50 does not exist
7 exists in the vector
The position of 7 using lower_bound 1
The position of 7 using upper_bound 2