Submission #240731

#	Time	Username	Problem	Language	Result	Execution time	Memory
240731		thecodingwizard	Flood (IOI07_flood)	C++11	23 / 100	643 ms	22064 KiB

flood

#include <bits/stdc++.h>

using namespace std;

#define ii pair<int, int>
#define f first
#define s second

struct Wall {
    int a, b;
    int idx;

    bool operator<(const Wall &other) const {
        if (a == other.a) return b < other.b;
        return a < other.a;
    }
};

int n;
ii A[100000];
vector<int> graph[100000];
vector<Wall> walls;
set<Wall> sortedWalls;
bool vis[200000][2];
bool done[200000];
vector<int> justDone;

int cross(int a, int b, int c) {
    int w = A[b].f-A[a].f, x = A[b].s - A[a].s, y = A[c].f - A[b].f, z = A[c].s - A[b].s;
    int cross = w*z-x*y;
    return cross;
}

bool turnRight(int a, int b, int c) {
    return cross(a, b, c) < 0;
}
bool turnLeft(int a, int b, int c) {
    return cross(a, b, c) > 0;
}
bool goForward(int a, int b, int c) {
    return (A[a].f==A[b].f&&A[b].f==A[c].f&&(A[a].s<A[b].s&&A[b].s<A[c].s||A[a].s>A[b].s&&A[b].s>A[c].s))||(A[a].s==A[b].s&&A[b].s==A[c].s&&(A[a].f<A[b].f&&A[b].f<A[c].f||A[a].f>A[b].f&&A[b].f>A[c].f));
}

void go(int u, int dir) {
    // cout << "go: " << walls[u].a << "," << walls[u].b << " " << dir << endl;
    if (vis[u][dir]) return;
    vis[u][dir] = true;
    justDone.push_back(u);
    Wall w = walls[u];
    sortedWalls.erase(w);

    int prvNode = dir == 0 ? w.b : w.a;
    int node = dir == 0 ? w.a : w.b;

    // right
    for (int wID : graph[node]) {
        int nxtNode = walls[wID].a == node ? walls[wID].b : walls[wID].a;
        int nxtDir = walls[wID].a == nxtNode ? 0 : 1;
        if (!done[wID] && turnRight(prvNode, node, nxtNode)) {
            return go(wID, nxtDir);
        }
    }
    
    // forward
    for (int wID : graph[node]) {
        int nxtNode = walls[wID].a == node ? walls[wID].b : walls[wID].a;
        int nxtDir = walls[wID].a == nxtNode ? 0 : 1;
        if (!done[wID] && goForward(prvNode, node, nxtNode)) {
            return go(wID, nxtDir);
        }
    }
    
    // left
    for (int wID : graph[node]) {
        int nxtNode = walls[wID].a == node ? walls[wID].b : walls[wID].a;
        int nxtDir = walls[wID].a == nxtNode ? 0 : 1;
        if (!done[wID] && turnLeft(prvNode, node, nxtNode)) {
            return go(wID, nxtDir);
        }
    }
    
    // back
    for (int wID : graph[node]) {
        int nxtNode = walls[wID].a == node ? walls[wID].b : walls[wID].a;
        int nxtDir = walls[wID].a == nxtNode ? 0 : 1;
        if (!done[wID]) return go(wID, nxtDir);
    }
}

int main() {
    int n; cin >> n;
    for (int i = 0; i < n; i++) cin >> A[i].f >> A[i].s;
    int w; cin >> w;
    for (int i = 0; i < w; i++) {
        int a, b; cin >> a >> b; --a; --b;
        sortedWalls.insert({a,b,i});
        walls.push_back({a,b,i});
        graph[a].push_back(i);
        graph[b].push_back(i);
        vis[i][0] = vis[i][1] = false;
        done[i] = false;
    }

    while (!sortedWalls.empty()) {
        // cout << "=== new go ===" << endl;
        go(sortedWalls.begin()->idx, 0);
        for (int x : justDone) done[x] = true;
        justDone.clear();
    }

    vector<int> ans;
    for (int i = 0; i < w; i++) {
        if (vis[i][0] && vis[i][1]) {
            ans.push_back(i);
        }
    }
    cout << ans.size() << endl;
    for (int i = 0; i < ans.size(); i++) {
        cout << ans[i]+1 << endl;
    }

    return 0;
}

Compilation message (stderr)

flood.cpp: In function 'bool goForward(int, int, int)':
flood.cpp:41:59: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
     return (A[a].f==A[b].f&&A[b].f==A[c].f&&(A[a].s<A[b].s&&A[b].s<A[c].s||A[a].s>A[b].s&&A[b].s>A[c].s))||(A[a].s==A[b].s&&A[b].s==A[c].s&&(A[a].f<A[b].f&&A[b].f<A[c].f||A[a].f>A[b].f&&A[b].f>A[c].f));
                                                           ^
flood.cpp:41:155: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
     return (A[a].f==A[b].f&&A[b].f==A[c].f&&(A[a].s<A[b].s&&A[b].s<A[c].s||A[a].s>A[b].s&&A[b].s>A[c].s))||(A[a].s==A[b].s&&A[b].s==A[c].s&&(A[a].f<A[b].f&&A[b].f<A[c].f||A[a].f>A[b].f&&A[b].f>A[c].f));
                                                                                                                                                           ^
flood.cpp: In function 'int main()':
flood.cpp:118:23: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for (int i = 0; i < ans.size(); i++) {
                     ~~^~~~~~~~~~~~

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