cpp/references/vector

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Description
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In this exercise we improve an order of growth by using references.
This program computes the millionth <i>harmonic number</i>,
$$H_{1000000} = 1/1 + 1/2 + \cdots + 1/100000.$$
It adds the numbers in reverse order to get more numerical stability.

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Choices
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Correct answer
Template / Reference solution

Template / Reference solution

#include <iostream>
#include <vector>
using namespace std;

// function to get Kth entry from end of vector
// K=0 is last entry, K=1 is second-last, etc
double kth_last_entry(\[vector<double>& vec\show:vector<double> vec]\, int K) {
return vec[vec.size()-K-1];
}

int main() {
// create array 1/1, 1/2, ... 1/100000
vector<double> values;
for (int i=1; i<=100000; i++)
values.push_back(1.0/i);

// add it in reverse order
double sum = 0;
for (int K=0; K<100000; K++)
sum += kth_last_entry(values, K);
cout << sum << endl;
}

Java test suite
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json list of stdin/args tests
e.g. [{"stdin":"hi", "args":["4", "5"]}, {"stdin":"noargs"}]
to just run once with no input use [{}]

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{}
]

C++ test suite
See manual

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Property	Value
Description html markup shown to student	In this exercise we improve an order of growth by using references. This program computes the millionth <i>harmonic number</i>, $$H_{1000000} = 1/1 + 1/2 + \cdots + 1/100000.$$ It adds the numbers in reverse order to get more numerical stability.
Epilogue html markup shown when solved	remove
Public permissions	remove
Remarks Comments, history, license, etc.	remove
Engine
Choices json list of string, bool pairs e.g. `[["good", true], ["bad", false]]`
Correct answer
Template / Reference solution
Template / Reference solution	#include <iostream> #include <vector> using namespace std; // function to get Kth entry from end of vector // K=0 is last entry, K=1 is second-last, etc double kth_last_entry(\[vector<double>& vec\show:vector<double> vec]\, int K) { return vec[vec.size()-K-1]; } int main() { // create array 1/1, 1/2, ... 1/100000 vector<double> values; for (int i=1; i<=100000; i++) values.push_back(1.0/i); // add it in reverse order double sum = 0; for (int K=0; K<100000; K++) sum += kth_last_entry(values, K); cout << sum << endl; }
Java test suite See manual
C++ test suite json list of stdin/args tests e.g. `[{"stdin":"hi", "args":["4", "5"]}, {"stdin":"noargs"}]` to just run once with no input use `[{}]`	[ {} ]
C++ test suite See manual
Forbidden substrings json list of strings e.g. `["for","while"]`	remove
Solution visibility	remove
Java imports json list of importables e.g. `["java.util.*"]`	remove
Override Java classname else defaults to websheet name	remove
Dependent on other websheets? json list of websheet names in this folder e.g. `["DataStructure"]`	remove
Is example? i.e., just a demo	remove
Add compiler flag(s) json list of flags e.g. `["-Wno-unused-variable"]`	remove
Remove default compiler flag(s) json list of flags see default_cppflags e.g. `["-Wno-write-strings"]`	remove

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