Kickstart 2022 (Round D), Problem A

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My submission gives WA without using cout<<fixed<<setprecision. Since the median needs atmost 1 decimal place of precision, this feels weird. Any explanations?

Code which will give WA on removing fixedprecision

#include <bits/stdc++.h>
// #include <ext/pb_ds/assoc_container.hpp>
// #include <ext/pb_ds/tree_policy.hpp>

// using namespace __gnu_pbds;

// template <class T>
// using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

using namespace std;

template <class X, class Y>
ostream &operator<<(ostream &os, pair<X, Y> const &p)
{
    return os << "(" << p.first << ", " << p.second << ") ";
}
template <class Ch, class Tr, class Container>
basic_ostream<Ch, Tr> &operator<<(basic_ostream<Ch, Tr> &os, Container const &x)
{
    os << "[ ";
    for (auto &y : x)
        os << y << ", ";
    return os << "]\n";
}

#define int long long
#define len(a) (int)a.size()
const long long INF = 1e18;
const double EPS = 1e-9;
const int di[8] = {1, 0, -1, 0, 1, -1, -1, 1};
const int dj[8] = {0, 1, 0, -1, 1, 1, -1, -1};
// dp?, graph?, bs on answer?, compress/sort queries?, stupid observation?
int solve_case()
{
    int n, m;
    cin >> n >> m;
    vector<int> a(n);
    for (int i = 0; i < n; i++)
        cin >> a[i];
    double ans = 0;
    vector<int> rest;
    sort(a.begin(), a.end());
    for (int i = 0; i < n; i++)
    {
        if (i < n - m + 1)
            rest.push_back(a[i]);
        else
            ans += a[i];
    }
    int k = len(rest);
    ans += (rest[(k - 1) / 2] + rest[k / 2]) / 2.0;
    cout << ans << '\n';
    return 0;
}

int32_t main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int t = 1;
    cin >> t;
    cout << fixed << setprecision(12);
    for (int _ = 1; _ <= t; _++)
    {
        cout << "Case #" << _ << ": ";
        solve_case();
    }
    return 0;
}

Comments (13)

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imtiyazrasool92

4 years ago, hide # |

← Rev. 3 →

-13

~~if the length of rest is odd than you have to add middle element~~

→ Reply

justaninactivealt

4 years ago, hide # ^ |

The expression (rest[(k - 1) / 2] + rest[k / 2]) / 2.0 gives the median regardless. Give it a try.

~~Oh actually you are getting WA because you didn't added the case where M == N. the rest array will be empty~~

WAtoAC2001

The rest vector will still have 1 element in it in that case as i<(n-m+1) so i<1 in the for loop while inserting elements in rest

← Rev. 2 →

i don't understood than why this code got AC

#include <bits/stdc++.h>
// #include <ext/pb_ds/assoc_container.hpp>
// #include <ext/pb_ds/tree_policy.hpp>

// using namespace __gnu_pbds;

// template <class T>
// using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

using namespace std;

template <class X, class Y>
ostream &operator<<(ostream &os, pair<X, Y> const &p)
{
    return os << "(" << p.first << ", " << p.second << ") ";
}
template <class Ch, class Tr, class Container>
basic_ostream<Ch, Tr> &operator<<(basic_ostream<Ch, Tr> &os, Container const &x)
{
    os << "[ ";
    for (auto &y : x)
        os << y << ", ";
    return os << "]\n";
}

#define int long long
#define len(a) (int)a.size()
const long long INF = 1e18;
const double EPS = 1e-9;
const int di[8] = {1, 0, -1, 0, 1, -1, -1, 1};
const int dj[8] = {0, 1, 0, -1, 1, 1, -1, -1};
// dp?, graph?, bs on answer?, compress/sort queries?, stupid observation?
int solve_case()
{
    int n, m;
    cin >> n >> m;
    vector<int> a(n);
    for (int i = 0; i < n; i++)
        cin >> a[i];
    double ans = 0;
    vector<int> rest;
    sort(a.begin(), a.end());
    for (int i = 0; i < n; i++)
    {
        if (i < n - m + 1)
            rest.push_back(a[i]);
        else
            ans += a[i];
    }
    int k = len(rest);
    if (k % 2)
        ans += rest[k / 2];
    else if (k)
        ans += (rest[k / 2] + rest[k / 2 - 1]) / 2.0;
    cout << ans << '\n';
    return 0;
}

int32_t main()
{
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    int t = 1;
    cin >> t;
    cout << fixed << setprecision(12);
    for (int _ = 1; _ <= t; _++)
    {
        cout << "Case #" << _ << ": ";
        solve_case();
    }
    return 0;
}

killpop

+21

Faced the same issue.

hihihizaru

I think it's because your code doesn't always print decimal point(.). See section "How does Kick Start handle real numbers? "

over_thinkerr

i also faced same issue

subhadeeppan07

bad question

JackPa

+20

Okay, you have put the code with setprecision included, this may cause some confusion I think. If you have a piece of code giving WA, i think it d be better to put the version that gives WA to not cause confusion.

About WA, this may be because of scientific notation. Without setprecision if the answer is 10^9 it ll output "1e+09", instead of the desired 1000000000 because its type is double.

Sorry for the confusion. Thanks for the explanation.

Auto comment: topic has been updated by justaninactivealt (previous revision, new revision, compare).

kostka

+12

Without fixed in C++ your program often prints results in scientific notation:

	double ans = 123456789;
	cout << ans << "\n";
        // will print 1.23457e+08
	cout << fixed << ans << "\n";
        // will print 123456789.000000

The first one differs from the expected answer by 211 (123457000-123456789).

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