Submission #515132

#	Time	Username	Problem	Language	Result	Execution time	Memory
515132		SHZhang	Roller Coaster Railroad (IOI16_railroad)	C++14	100 / 100	150 ms	17432 KiB

railroad

#include "railroad.h"
#include <algorithm>
#include <utility>

using namespace std;

vector<pair<int, int> > locs;

int uf[400005];
int pre[400005];

int fin(int x)
{
    if (uf[x] == x) return x;
    return uf[x] = fin(uf[x]);
}

void un(int x, int y)
{
    x = fin(x); y = fin(y);
    if (x != y) uf[x] = y;
}

long long plan_roller_coaster(vector<int> s, vector<int> t) {
    int n = (int)s.size();
    for (int i = 0; i < 2 * n; i++) {
        uf[i] = i; pre[i] = -1;
    }
    for (int i = 0; i < n; i++) locs.push_back(make_pair(s[i], i + 1));
    for (int i = 0; i < n; i++) locs.push_back(make_pair(t[i], -i - 1));
    sort(locs.begin(), locs.end());
    for (int i = 0; i < 2 * n; i++) {
        int idx;
        if (locs[i].second < 0) {
            idx = -locs[i].second - 1;
        } else {
            idx = locs[i].second - 1;
        }
        //printf("! %d %d\n", locs[i].first, idx);
        if (pre[idx] != -1) {
            un(i, pre[idx]);
            //printf("! %d %d\n", i, pre[idx]);
        } else {
            pre[idx] = i;
        }
    }
    int rightcnt = 1;
    vector<pair<int, int> > edges;
    long long ans = 0;
    for (int i = 0; i < 2 * n; i++) {
        if (locs[i].second < 0) {
            rightcnt++;
        } else {
            rightcnt--;
        }
        if (!rightcnt) {
            edges.push_back(
                make_pair(locs[i+1].first - locs[i].first, i));
        } else if (i != 2 * n - 1) {
            un(i, i+1);
            //printf("add %d %d\n", i, rightcnt);
            if (rightcnt < 0) ans += (long long)(-rightcnt) *
                (long long)(locs[i+1].first - locs[i].first);
        }
    }
    sort(edges.begin(), edges.end());
    for (int i = 0; i < edges.size(); i++) {
        if (fin(edges[i].second) != fin(edges[i].second + 1)) {
            ans += (long long)edges[i].first;
            un(edges[i].second, edges[i].second + 1);
        }
    }
    return ans;
}

Compilation message (stderr)

railroad.cpp: In function 'long long int plan_roller_coaster(std::vector<int>, std::vector<int>)':
railroad.cpp:67:23: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<std::pair<int, int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   67 |     for (int i = 0; i < edges.size(); i++) {
      |                     ~~^~~~~~~~~~~~~~

• Subtask 1: 11 / 11
• Subtask 2: 23 / 23
• Subtask 3: 30 / 30
• Subtask 4: 36 / 36