Submission #745624

#	Time	Username	Problem	Language	Result	Execution time	Memory
745624		MilosMilutinovic	Beads and wires (APIO14_beads)	C++14	0 / 100	3 ms	4948 KiB

beads

#include <bits/stdc++.h>
using namespace std;
#define ll long long
const int N = 2e5 + 10;
const ll inf = 1e16;
ll dp[N][2][2]; // node, par edge, bad path
vector<pair<int, int>> g[N];
int n, w[N];
void setup() {
    for (int i = 1; i <= n; i++)
        for (int x = 0; x < 2; x++)
            for (int y = 0; y < 2; y++)
                dp[i][x][y] = -inf;
}
void solve(int x, int fa, int uw) {
    vector<int> ch;
    for (auto& p : g[x]) {
        int y = p.first;
        if (y == fa) continue;
        w[y] = p.second;
        solve(y, x, w[y]);
        ch.push_back(y);
    }
    if (ch.empty()) {
        dp[x][0][0] = 0;
        return;
    }

    // don't take x
    {
        vector<ll> cur(2, -inf);
        cur[0] = 0;
        for (int y : ch) {
            vector<ll> ndp(2, -inf);
            ndp[0] = max(ndp[0], cur[0] + dp[y][0][0]);
            ndp[0] = max(ndp[0], cur[0] + dp[y][1][0]);

            ndp[1] = max(ndp[1], cur[0] + dp[y][0][1]);
            ndp[1] = max(ndp[1], cur[0] + dp[y][1][1]);

            ndp[1] = max(ndp[1], cur[1] + dp[y][0][0]);
            ndp[1] = max(ndp[1], cur[1] + dp[y][1][0]);
            swap(cur, ndp);
        }
        dp[x][0][0] = cur[0];
        dp[x][0][1] = cur[1];
    }

    // take x, from bad path
    {
        vector<vector<ll>> cur(3, vector<ll>(2, -inf));
        cur[0][0] = 0;
        for (int y : ch) {
            vector<vector<ll>> ndp(3, vector<ll>(2, -inf));

            // don't take y
            for (int i = 0; i < 3; i++) {
                for (int j = 0; j < 2; j++) {
                    ndp[i][j] = max(ndp[i][j], cur[i][j] + dp[y][0][0]);
                    ndp[i][j] = max(ndp[i][j], cur[i][j] + dp[y][1][0]);
                }
            }

            // take y
            for (int i = 0; i < 2; i++) {
                for (int j = 0; j < 2; j++) {
                    for (int o = 0; o < 2; o++) {
                        if (j + o == 2) continue;
                        ndp[i + 1][j + o] = max(ndp[i + 1][j + o], cur[i][j] + dp[y][0][o] + w[y]);
                    }
                }
            }

            swap(cur, ndp);
        }
        dp[x][0][1] = max(cur[2][0], cur[2][1]);
    }

    // take x, no bad path
    {
        vector<vector<ll>> cur(2, vector<ll>(2, -inf));
        cur[0][0] = uw;
        for (int y : ch) {
            vector<vector<ll>> ndp(2, vector<ll>(2, -inf));

            // don't take y
            for (int i = 0; i < 2; i++) {
                for (int j = 0; j < 2; j++) {
                    for (int o = 0; o < 2; o++) {
                        if (j + o == 2) continue;
                        ndp[i][j + o] = max(ndp[i][j + o], cur[i][j] + dp[y][0][o]);
                        ndp[i][j + o] = max(ndp[i][j + o], cur[i][j] + dp[y][1][o]);
                    }
                }
            }

            // take y
            for (int i = 0; i < 1; i++) {
                for (int j = 0; j < 2; j++) {
                    for (int o = 0; o < 2; o++) {
                        if (j + o == 2) continue;
                        ndp[i + 1][j + o] = max(ndp[i + 1][j + o], cur[i][j] + dp[y][0][o] + w[y]);
                    }
                }
            }

            swap(cur, ndp);
        }
        dp[x][1][0] = cur[1][0];
        dp[x][1][1] = cur[1][1];
    }

}
int main() {
    scanf("%d", &n);
    for (int i = 1; i < n; i++) {
        int a, b, c;
        scanf("%d%d%d", &a, &b, &c);
        g[a].push_back({b, c});
        g[b].push_back({a, c});
    }
    setup();
    solve(1, 1, -inf / 10);
    printf("%lld\n", max(dp[1][0][0], dp[1][0][1]));
    return 0;
}

/*
5
1 2 10
1 3 40
1 4 15
1 5 20

60

10
4 10 2
1 2 21
1 3 13
6 7 1
7 9 5
2 4 3
2 5 8
1 6 55
6 8 34

140


9
1 3 100
2 3 100
3 7 1
4 5 100
4 6 100
7 4 1
8 7 100
9 7 100
*/

Compilation message (stderr)

beads.cpp: In function 'int main()':
beads.cpp:123:22: warning: overflow in conversion from 'long long int' to 'int' changes value from '-1000000000000000' to '1530494976' [-Woverflow]
  123 |     solve(1, 1, -inf / 10);
      |                 ~~~~~^~~~
beads.cpp:115:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  115 |     scanf("%d", &n);
      |     ~~~~~^~~~~~~~~~
beads.cpp:118:14: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  118 |         scanf("%d%d%d", &a, &b, &c);
      |         ~~~~~^~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 0 / 13
• Subtask 2: 0 / 15
• Subtask 3: 0 / 29
• Subtask 4: 0 / 43