获取STL向量中大于值的元素的所有位置 [英] Get all positions of elements in STL vector that are greater than a value

问题描述

我想知道如何找到验证某个条件(例如大于)的元素的索引位置.例如，如果我有一个整数值的向量

  vector< int>V; 

V包含值 3 2 5 8 2 1 10 4 7

，我想获取所有大于5的元素的索引位置.我知道 std :: find_if ，但是根据文档，它只是找到满足条件的第一个元素.

解决方案

循环 std :: find_if ，从您上次停止的地方开始.

示例(查看它的工作原理):

  std :: vector< size_t>结果;auto it = std :: find_if(std :: begin(v)，std :: end(v)，[](int i){return i> 5;});while(它！= std :: end(v)){results.emplace_back(std :: distance(std :: begin(v)，it));它= std :: find_if(std :: next(it)，std :: end(v)，[](int i){return i> 5;})；} 

首先，我们用第一个结果设置迭代器.如果找不到，则while循环将永远不会执行.否则，将存储索引位置( std :: distance 本质上是更通用的 it-std :: begin(v))，然后继续搜索.

I would like to know how can I find the index positions of elements that verify a certain condition (for example greater than). For example if I have a vector of int values

vector<int> V;

V contains the values 3 2 5 8 2 1 10 4 7

and I want to get all the index positions of elements that are greater than 5. I know std::find_if but according to the documentation it just finds the first element that satisfies a condition.

解决方案

Loop std::find_if, starting from where you stopped last time.

Sample (see it work):

std::vector<size_t> results;

auto it = std::find_if(std::begin(v), std::end(v), [](int i){return i > 5;});
while (it != std::end(v)) {
   results.emplace_back(std::distance(std::begin(v), it));
   it = std::find_if(std::next(it), std::end(v), [](int i){return i > 5;});
}

First we set up the iterator with the first result. If it's not found, the while loop never executes. Otherwise, the index position is stored (std::distance is basically a more generic it - std::begin(v)), and the search continues onward.

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