HDU 4123

Posted 2020-10-03

实际上是一个 HDU 2196 加上RMQ的题。

#include <algorithm>
#include <cstdio>
#include <cstring>
#include <vector>

#define Max 1000001
#define MAXN 1000005
#define MOD 1000000007
#define rin freopen("in.txt","r",stdin)
#define rout freopen("1.out","w",stdout)
#define Del(a,b) memset(a,b,sizeof(a))
typedef long long LL;
using namespace std;
const int N = 50100;
int T;
struct Node {
    int to;
    int cap;
};
vector<Node> v[N];
int dp[N][4];
int maxsum[N][25];
int minsum[N][25];
int logg[N];
void Init() {
    logg[0] = -1;
    for (int i = 1; i <= N; i++)
        logg[i] = logg[i >> 1] + 1; //logg[i]表示int logg2(i)  
}
void dfs1(int father) {
    int mast = 0;
    int maer = 0;
    for (int i = 0; i < v[father].size(); i++) {
        Node child = v[father][i];
        dfs1(child.to);
        int cost = dp[child.to][0] + child.cap;
        if (cost >= mast) {
            maer = mast;
            mast = cost;
        } else if (cost > maer) {
            maer = cost;
        }
    }
    dp[father][0] = mast;
    dp[father][1] = maer;
}
void dfs2(int root) {
    for (int i = 0; i < v[root].size(); i++) {
        Node child = v[root][i];
        dp[child.to][2] = max(dp[root][2],
                dp[child.to][0] + child.cap == dp[root][0] ?
                        dp[root][1] : dp[root][0]) + child.cap;
        dfs2(child.to);
    }
}
void RMQ(int n)
{
    for (int j = 1; j < 20; ++j)
        for (int i = 1; i <= n; ++i)
            if (i + (1 << j) - 1 <= n) {
                maxsum[i][j] = max(maxsum[i][j - 1],
                        maxsum[i + (1 << (j - 1))][j - 1]);
                minsum[i][j] = min(minsum[i][j - 1],
                        minsum[i + (1 << (j - 1))][j - 1]);
            }
}
int rmq_min(int l, int r) {
    int tmp = logg[r - l + 1];
    int a = max(maxsum[l][tmp], maxsum[r - (1 << tmp) + 1][tmp]);
    int b = min(minsum[l][tmp], minsum[r - (1 << tmp) + 1][tmp]);
    return a - b;
}
int main() {

    rin;
    int n, m;
    Init();
    while (scanf("%d%d", &n, &m) && n + m) {
        for (int i = 1; i <= n - 1; i++) {
            int x, y, z;
            scanf("%d%d%d", &x, &y, &z);
            int maxnode = max(x, y);
            int minnode = min(x, y);
            Node tmp;
            tmp.cap = z;
            tmp.to = maxnode;
            v[minnode].push_back(tmp);
        }
        Del(dp, 0);
        dfs1(1);
        dp[1][2] = 0;
        dfs2(1);
        for (int i = 1; i <= n; i++) {
            maxsum[i][0] = max(dp[i][0], dp[i][2]);
            minsum[i][0] = max(dp[i][0], dp[i][2]);
        }
        RMQ(n);
        for (int i = 0; i < m; i++) {
            int Q;
            scanf("%d", &Q);
            int l = 1, r = 1, ans = 0;
            while (l <= n && r <= n) {
                if (rmq_min(l, r) <= Q) {
                    ans = max(ans, r - l + 1);
                    r++;
                } else
                    l++;
            }
            printf("%d\n", ans);
        }
        for (int i = 1; i <= n; i++) {
            v[i].clear();
        }
    }
    return 0;
}