如何使用的算法，以填补载体的载体 [英] How to use algorithms to fill vector of vectors

问题描述

我

typedef std::vector<int> IVec;
typedef std::vector<IVec> IMat;

和我想知道我可以填写一个 IMAT 通过使用std算法，即如何做到少code以下（所有 IVEC 取值具有相同的大小）？

and I would like to know how I can fill an IMat by using std algorithms, ie how to do the following with less code (all the IVecs have the same size) ?

void fill(IMat& mat){
    for (int i=0;i<mat.size();i++){
        for (int j=0;j<mat[i].size();j++){
            mat[i][j] = i*j;
        }
    }
}

PS：已经是一个方式来填补的矩阵与一个常数，就帮我。而preferably用pre-C ++ 11的算法。

PS: already a way to fill the matrix with a constant would help me. And preferably with pre-C++11 algorithms.

推荐答案

最好的解决办法是，你已经实现了的。这需要使用优势我 / Ĵ既偏移和作为输入来计算的算法。

The best solution is the one that you have already implemented. It takes advantage of using i/j as both offsets and as inputs to compute the algorithm.

标准算法将不得不使用迭代器的元素的和的保持计数器。此数据镜像是一个问题的明确信号。不过，这是可以做到，即使是在同一行，如果你想成为奇特的：

Standard algorithms will have to use iterators for the elements and maintain counters. This data mirroring as a sure sign of a problem. But it can be done, even on one line if you wanna be fancy:

for_each(mat.begin(), mat.end(), [&](auto& i) { static auto row = 0; auto column = 0; generate(i.begin(), i.end(), [&]() { return row * column++; }); ++row; });

但由于规定刚刚引起它可以做并不意味着它应该做的。接近这一点的最好办法是在为 -loop。即使是做一行是可能的，如果那是你的事：

But as stated just cause it could be done doesn't mean that it should be done. The best way to approach this is the for-loop. Even doing it on one line is possible if that's your thing:

for(auto i = 0U;i < mat.size();i++) for(auto j = 0U;j < mat[i].size();j++) mat[i][j] = i*j;

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顺便说一下我的标准算法工作正常铛3.7.0 ，的 GCC 5.1 和基于Visual Studio 2015年不过的 previously我用转换，而不是生成 。而且似乎有一些<一href="http://stackoverflow.com/questions/33285103/capturing-a-lambdas-static-in-a-nested-lambda">implementation在GCC 5.1和Visual Studio 2015年与拉姆达范围静态变量。

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Incidentally my standard algorithm works fine on Clang 3.7.0, gcc 5.1, and on Visual Studio 2015. However previously I used transform rather than generate. And there seem to be some implementation bugs in gcc 5.1 and Visual Studio 2015 with the captures of lambda scope static variables.

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