Submission #583750

#	Time	Username	Problem	Language	Result	Execution time	Memory
583750		InternetPerson10	Sorting (IOI15_sorting)	C++17	74 / 100	1053 ms	24784 KiB

sorting

#include "sorting.h"
#include <bits/stdc++.h>

using namespace std;

bool trySwapPairs(int n, int S[], int m, int X[], int Y[], int P[], int Q[]) {
    vector<int> targetArr(n);
    vector<int> revInd(n);
    int countMatches = 0;
    for(int i = 0; i < n; i++) {
        targetArr[i] = i;
        if(S[i] == i) countMatches++;
    }
    for(int i = m-1; i >= 0; i--) {
        swap(targetArr[X[i]], targetArr[Y[i]]);
    }
    for(int i = 0; i < n; i++) {
        revInd[targetArr[i]] = i;
    }
    set<int> notGood; // Indices of places where no match
    for(int i = 0; i < n; i++) {
        if(S[i] != targetArr[i]) notGood.insert(i);
    }
    auto swapTwo = [&](int i, int a, int b) {
        if(a == S[a]) countMatches--;
        if(b == S[b]) countMatches--;
        swap(S[a], S[b]);
        P[i] = a; Q[i] = b;
        if(a == S[a]) countMatches++;
        if(b == S[b]) countMatches++;
    };
    for(int i = 0; i < m; i++) {
        if(countMatches == n) {
            m = i;
            break;
        }
        if(X[i] != Y[i]) {
            int x = (int)notGood.count(X[i]);
            int y = (int)notGood.count(Y[i]);
            if(X[i] == S[X[i]]) countMatches--;
            if(Y[i] == S[Y[i]]) countMatches--;
            swap(revInd[targetArr[X[i]]], revInd[targetArr[Y[i]]]);
            swap(targetArr[X[i]], targetArr[Y[i]]);
            swap(S[X[i]], S[Y[i]]);
            notGood.erase(X[i]);
            notGood.erase(Y[i]);
            if(x) notGood.insert(Y[i]);
            if(y) notGood.insert(X[i]);
            if(X[i] == S[X[i]]) countMatches++;
            if(Y[i] == S[Y[i]]) countMatches++;
        }
        if(notGood.size() == 0) {
            swapTwo(i, 0, 0);
            continue;
        }
        int a = *(notGood.begin());
        int b = revInd[S[a]];
        swapTwo(i, a, b);
        assert(S[b] == targetArr[b]);
        if(S[a] == targetArr[a]) notGood.erase(a);
        if(S[b] == targetArr[b]) notGood.erase(b);
    }
    return (countMatches == n);
}

int findSwapPairs(int n, int R[], int m, int X[], int Y[], int P[], int Q[]) {
    int V[200001];
    int l = -1, r = m;
    while(l != r - 1) {
        for(int i = 0; i < n; i++) {
            V[i] = R[i];
        }
        int mid = (l + r + 1) / 2;
        if(trySwapPairs(n, V, mid, X, Y, P, Q)) r = mid;
        else l = mid;
    }
    trySwapPairs(n, R, r, X, Y, P, Q);
    return r;
}

• Subtask 1: 8 / 8
• Subtask 2: 12 / 12
• Subtask 3: 16 / 16
• Subtask 4: 18 / 18
• Subtask 5: 20 / 20
• Subtask 6: 0 / 26