Submission #280105

#	Time	Username	Problem	Language	Result	Execution time	Memory
280105		ec1117	Arranging Shoes (IOI19_shoes)	C++17	100 / 100	106 ms	12400 KiB

shoes

/**
 * Description: range sum queries and point updates for $D$ dimensions
 * Source: https://codeforces.com/blog/entry/64914
 * Verification: SPOJ matsum
 * Usage: \texttt{BIT<int,10,10>} gives 2D BIT
 * Time: O((\log N)^D)
 */


#include "bits/stdc++.h"
#include "shoes.h"
using namespace std;

typedef long long ll;
typedef vector<int> vi;
typedef pair<int,int> pi;

#define pb push_back
#define mp make_pair
#define sz(v) ((int)(v).size())

const int MAXN = 200005;

struct bit{
    int tree[MAXN];
    void add(int x, int v){
        for(int i=x; i<MAXN; i+=i&-i) tree[i] += v;
    }
    int query(int x){
        int ret = 0;
        for(int i=x; i; i-=i&-i) ret += tree[i];
        return ret;
    }
}bit;


vector<pi> order[MAXN];
vector<pi> calc;
ll count_swaps(vector<int> s){
    int n = sz(s) / 2;
    ll ret=0;
    for(int i=0;i<sz(s);i++)
        order[abs(s[i])].push_back(mp(s[i], i));
    for(int i=1;i<=MAXN;i++){
        sort(order[i].begin(), order[i].end());
        for(int j=0;j<order[i].size()/2;j++){
            int l = order[i][j].second;
            int r = order[i][j + sz(order[i])/2].second;
            if(l>r) {
                ret++;
                swap(l,r);
            }
            calc.push_back(mp(l + 1, r + 1));
        }
    }
    for(int i=1; i<=2*n; i++) bit.add(i, 1);
    sort(calc.begin(),calc.end());
    for(pi x:calc){
        ret += bit.query(x.second) - bit.query(x.first) -1;
        bit.add(x.second,-1);
        bit.add(x.first,-1);
    }
    return ret;
}

Compilation message (stderr)

shoes.cpp: In function 'll count_swaps(std::vector<int>)':
shoes.cpp:46:22: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   46 |         for(int j=0;j<order[i].size()/2;j++){
      |                     ~^~~~~~~~~~~~~~~~~~

• Subtask 1: 10 / 10
• Subtask 2: 20 / 20
• Subtask 3: 20 / 20
• Subtask 4: 15 / 15
• Subtask 5: 20 / 20
• Subtask 6: 15 / 15