二叉搜索C ++ STL [英] Binary Search C++ STL

问题描述

我有一个unordered_map的向量，它是基于我定义的比较器函数排序的。我想使用二进制搜索来寻找一个值使用比较器函数，以及。但是，二叉搜索只返回bool，我需要结果的索引/迭代器。我可以做什么？

I have a vector of unordered_map which is sorted based on the comparer function I defined. I would like to use binary search to look for one of the value using the comparer function as well. However, binary search only return bool and I need the index / iterator of the result. What could I do?

推荐答案

#include <algorithm>
using namespace std;

//!!!!!   a must be sorted using cmp. Question indicates that it is.        
it = lower_bound(a.begin, a.end(), value, cmp);

//Check that we have actually found the value. 
//If the requested value is missing
//then we will have the value before where the requested value 
//would be inserted.
if(it == a.end() || !cmp(*it, value))
{
   //element not found
} 
else
{
   //element found
}

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