c++更快的if else语句

c++ faster if else statements

本文关键字：else 语句 if c++      更新时间：2023-10-16

我是一个新的c++用户，并编写了一个与其他函数一起工作的代码。我需要修改代码与if &else if语句，这导致整个代码运行4.6333分钟，而修改前为0.61分钟(注意，这些持续时间是针对整个代码的，而不是针对下面我粘贴的示例)。

下面以"only"修改过的部分为例(可以在c++中单独运行)。

谁有任何建议得到这个代码更快?

#include <iostream>
#include <vector>
#include <fstream>
#include <ctime>
using namespace std;
int main()
{
    static const double InflVecVals001[9] = { 100.0, 200.0, 300.0, 400.0, 500.0, 600.0, 700.0, 800.0, 900.0 };
    int FloorMnodeTagscol1[6] = { 11, 12, 13, 14, 15, 16 }; int FloorMnodeTagscol6[6] = { 61, 62, 63, 64, 65, 66 };
    int FloorMnodeTagscol2[6] = { 21, 22, 23, 24, 25, 26 }; int FloorMnodeTagscol7[6] = { 71, 72, 73, 74, 75, 76 };
    int FloorMnodeTagscol3[6] = { 31, 32, 33, 34, 35, 36 }; int FloorMnodeTagscol8[6] = { 81, 82, 83, 84, 85, 86 };
    int FloorMnodeTagscol4[6] = { 41, 42, 43, 44, 45, 46 }; int FloorMnodeTagscol9[6] = { 91, 92, 93, 94, 95, 96 };
    int FloorMnodeTagscol5[6] = { 51, 52, 53, 54, 55, 56 };
    int tagNode = 91;
    double fact;
    if ((tagNode == FloorMnodeTagscol1[0]) || (tagNode == FloorMnodeTagscol1[1]) || (tagNode == FloorMnodeTagscol1[2]) || (tagNode == FloorMnodeTagscol1[3]) || (tagNode == FloorMnodeTagscol1[4]) || (tagNode == FloorMnodeTagscol1[5]))
    {
        fact = InflVecVals001[0];
    }
    else if ((tagNode == FloorMnodeTagscol2[0]) || (tagNode == FloorMnodeTagscol2[1]) || (tagNode == FloorMnodeTagscol2[2]) || (tagNode == FloorMnodeTagscol2[3]) || (tagNode == FloorMnodeTagscol2[4]) || (tagNode == FloorMnodeTagscol2[5]))
    {
        fact = InflVecVals001[1];
    }
    else if ((tagNode == FloorMnodeTagscol3[0]) || (tagNode == FloorMnodeTagscol3[1]) || (tagNode == FloorMnodeTagscol3[2]) || (tagNode == FloorMnodeTagscol3[3]) || (tagNode == FloorMnodeTagscol3[4]) || (tagNode == FloorMnodeTagscol3[5]))
    {
        fact = InflVecVals001[2];
    }
    else if ((tagNode == FloorMnodeTagscol4[0]) || (tagNode == FloorMnodeTagscol4[1]) || (tagNode == FloorMnodeTagscol4[2]) || (tagNode == FloorMnodeTagscol4[3]) || (tagNode == FloorMnodeTagscol4[4]) || (tagNode == FloorMnodeTagscol4[5]))
    {
        fact = InflVecVals001[3];
    }
    else if ((tagNode == FloorMnodeTagscol5[0]) || (tagNode == FloorMnodeTagscol5[1]) || (tagNode == FloorMnodeTagscol5[2]) || (tagNode == FloorMnodeTagscol5[3]) || (tagNode == FloorMnodeTagscol5[4]) || (tagNode == FloorMnodeTagscol5[5]))
    {
        fact = InflVecVals001[4];
    }
    else if ((tagNode == FloorMnodeTagscol6[0]) || (tagNode == FloorMnodeTagscol6[1]) || (tagNode == FloorMnodeTagscol6[2]) || (tagNode == FloorMnodeTagscol6[3]) || (tagNode == FloorMnodeTagscol6[4]) || (tagNode == FloorMnodeTagscol6[5]))
    {
        fact = InflVecVals001[5];
    }
    else if ((tagNode == FloorMnodeTagscol7[0]) || (tagNode == FloorMnodeTagscol7[1]) || (tagNode == FloorMnodeTagscol7[2]) || (tagNode == FloorMnodeTagscol7[3]) || (tagNode == FloorMnodeTagscol7[4]) || (tagNode == FloorMnodeTagscol7[5]))
    {
        fact = InflVecVals001[6];
    }
    else if ((tagNode == FloorMnodeTagscol8[0]) || (tagNode == FloorMnodeTagscol8[1]) || (tagNode == FloorMnodeTagscol8[2]) || (tagNode == FloorMnodeTagscol8[3]) || (tagNode == FloorMnodeTagscol8[4]) || (tagNode == FloorMnodeTagscol8[5]))
    {
        fact = InflVecVals001[7];
    }
    else if ((tagNode == FloorMnodeTagscol9[0]) || (tagNode == FloorMnodeTagscol9[1]) || (tagNode == FloorMnodeTagscol9[2]) || (tagNode == FloorMnodeTagscol9[3]) || (tagNode == FloorMnodeTagscol9[4]) || (tagNode == FloorMnodeTagscol9[5]))
    {
        fact = InflVecVals001[8];
    }
    else
    {
        fact = 1.0;
    }
    //cout << "n tagnode:" << tagNode << endl;
    //cout << "n factor:" << fact << endl;
    cin.get();
    return 0;
}

对于您的示例代码，您可以简单地使用

if ((tagNode - 1) % 10 < 6 && 11 <= tagNode && tagNode <= 96) {
    fact = (tagNode / 10) * 100.;
} else {
    fact = 1.;
}

但是假设值不像您的示例中那样是简单的范围，并且您必须多次执行映射，您可以这样做:

static const std::map<int, double> m = {
    { 11, 100.}, {12, 100.}, {13, 100.}, {14, 100.}, {15, 100.}, {16, 100.},
    { 21, 200.}, {22, 200.}, {23, 200.}, {24, 200.}, {25, 200.}, {26, 200.},
    { 31, 300.}, {32, 300.}, {33, 300.}, {34, 300.}, {35, 300.}, {36, 300.},
    { 41, 400.}, {42, 400.}, {43, 400.}, {44, 400.}, {45, 400.}, {46, 400.},
    { 51, 500.}, {52, 500.}, {53, 500.}, {54, 500.}, {55, 500.}, {56, 500.},
    { 61, 600.}, {62, 600.}, {63, 600.}, {64, 600.}, {65, 600.}, {66, 600.},
    { 71, 700.}, {72, 700.}, {73, 700.}, {74, 700.}, {75, 700.}, {76, 700.},
    { 81, 800.}, {82, 800.}, {83, 800.}, {84, 800.}, {85, 800.}, {86, 800.},
    { 91, 900.}, {92, 900.}, {93, 900.}, {94, 900.}, {95, 900.}, {96, 900.}
};
auto it = m.find(tagNode);
fact = ((it != m.end()) ? it-> second : 1.);

演示

的
  • N log N用于地图构建(完成一次)。
  • log(N)搜索复杂度。

而不是线性搜索

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