Submission #631845

#	Time	Username	Problem	Language	Result	Execution time	Memory
631845		rainliofficial	Aliens (IOI16_aliens)	C++17	0 / 100	1 ms	212 KiB

aliens

#include "aliens.h"
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int, int> pii;
template<class T> bool ckmin(T& a, const T& b) { return b < a ? a = b, 1 : 0; }
template<class T> bool ckmax(T& a, const T& b) { return a < b ? a = b, 1 : 0; }
#define sz(x) (int)x.size()

const int MAXN = 2e5+5, INF = 1e9;

struct Point{
    int r, c, id, cnt;
    bool operator<(const Point& o) const{
        if (r != o.r){
            return r < o.r;
        }
        return c < o.c;
    }
};

bool byr(const Point& a, const Point& b){
    return a.r != b.r ? a.r < b.r : a.c > b.c;  // sort by smaller row, then by greater col
}

bool byc(const Point& a, const Point& b){
    return a.c != b.c ? a.c < b.c : a.r < b.r; // smaller col, smaller row
}

long long take_photos(int n, int m, int k, std::vector<int> r, std::vector<int> c) {
    // reflect the points under the diag
    vector<Point> arr;
    int tot = 0;
    set<Point> allPoints;
    for (int i=0; i<n; i++){
        if (r[i] > c[i]){
            swap(r[i], c[i]);
        }
        Point cur = {r[i], c[i], tot, 1};
        auto it = allPoints.find(cur);
        if (it != allPoints.end()){
            arr[(*it).id].cnt++;
        }else{
            arr.push_back(cur);
            allPoints.insert(cur);
            tot++;
        }
    }
    n = tot;
    sort(arr.begin(), arr.end(), byr);
    set<Point, decltype(&byc)> st(&byc);
    set<Point> seen;
    for (int i=0; i<n; i++){
        auto it = seen.lower_bound(arr[i]);
        if (it != seen.end()){
            Point upd = *it;
            upd.cnt++;
            seen.erase(it);
            seen.insert(upd);
        }else{
            seen.insert(arr[i]);
        }
    }

    arr.clear();
    for (Point x : seen){
        // cout << x.r << " " << x.c << " " << x.id << " " << x.cnt << "\n";
        arr.push_back(x);
    }

    n = sz(arr);
    // run dp
    vector<vector<int>> dp(n+1, vector<int>(k+1, INF)); // dp[i][j] = max cover up to ith point after taking j pictures
    for (int i=0; i<=k; i++) dp[0][i] = 0;
    for (int i=1; i<=n; i++){
        for (int j=1; j<=k; j++){
            for (int ip=1; ip<=i; ip++){
                ckmin(dp[i][j], dp[i-1][j-1] + (arr[i-1].c - arr[ip-1].r + 1)*(arr[i-1].c - arr[ip-1].r + 1));
            }
        }
    }
    return dp[n][k];
}



/**
 * Debugging checklist:
 * - Reset everything after each TC
 * - Integer overflow, index overflow
 * - Special cases?
 */

• Subtask 1: 0 / 4
• Subtask 2: 0 / 12
• Subtask 3: 0 / 9
• Subtask 4: 0 / 16
• Subtask 5: 0 / 19
• Subtask 6: 0 / 40