Codeforces1076E. Vasya and a Tree（dfs+离线+动态维护前缀和）

题目链接：传送门

题目：

E. Vasya and a Tree
time limit per test
 seconds
memory limit per test
 megabytes
input
standard input
output
standard output
 
Vasya has a tree consisting of n
vertices with root in vertex . At first all vertices has 
 
written on it.
 
Let d(i,j)
be the distance between vertices i and j, i.e. number of edges in the shortest path from i to j. Also, let's denote k-subtree of vertex x — set of vertices y
 
such that next two conditions are met:
 
    x
 
is the ancestor of y
(each vertex is the ancestor of itself);
d(x,y)≤k
 
    . 
 
Vasya needs you to process m
queries. The i-th query is a triple vi, di and xi. For each query Vasya adds value xi to each vertex from di-subtree of vi
 
.
 
Report to Vasya all values, written on vertices of the tree after processing all queries.
Input
 
The first line contains single integer n
(≤n≤⋅
 
) — number of vertices in the tree.
 
Each of next n−
lines contains two integers x and y (≤x,y≤n) — edge between vertices x and y
 
. It is guarantied that given graph is a tree.
 
Next line contains single integer m
(≤m≤⋅
 
) — number of queries.
 
Each of next m
lines contains three integers vi, di, xi (≤vi≤n, ≤di≤, ≤xi≤) — description of the i
 
-th query.
Output
 
Print n
integers. The i-th integers is the value, written in the i
 
-th vertex after processing all queries.
Examples
Input
Copy
 
Output
Copy
 
Input
Copy
 
Output
Copy
 
Note
 
In the first exapmle initial values in vertices are ,,,,
. After the first query values will be equal to ,,,,. After the second query values will be equal to ,,,,. After the third query values will be equal to ,,,,.

题目大意：

　　给定一棵有N个节点的有向树，根节点为1。

　　有M次操作，对以v_i为根的深度为d_i的子树上的所有节点权值加x_i。

　　1≤n，m≤3⋅10⁵，1 ≤ v_i ≤ n，0 ≤ d_i ≤ 10⁹，1 ≤ x_i ≤ 10⁹

思路：

　　离线处理，把每个更新都放到对应的vi上，然后从节点1开始dfs。

　　dfs时遇到一个节点后，把这个节点所有的“操作”都拿出来：

　　对于每个“操作”，更新当前深度到本次操作影响的最大深度[dep, dep+d_i]区间内的值加上x_i，回溯的时候再减掉x_i。这里可以用树状数组维护。

　　每个节点的答案就是被搜索到之后，“操作”结束之后的当前深度的值。

　　到这里就已经可以AC了。

　　但是树状数组的logn的复杂度还可以继续优化，用一个前缀和数组sum维护，更新[dep, dep+d_i]区间时，只要让sum[dep] += x_i，sum[dep+d_i+1] -= x_i，就可以实现整个区间的加减了。

　　有人问（就是我）：“中间的明明没有加上去啊？？？”

　　“。。。对，但是你是一个个跑过来的啊，把之前的前缀加过来不就好了？”（w神）

　　period。

UPDATE：

　　其实就是dfs的时候顺便维护前缀和，遇到当前深度的时候把当前深度的权值（可能是负的）都捡起来，然后进入下一层，回溯的时候再把捡起来的权值都丢掉。

代码：

#include <bits/stdc++.h>
 
using namespace std;
typedef long long ll;
const int MAX_NM = ;
 
int n, m, t, act;
string opt[];
string acts[];
ll F[MAX_NM], A[][MAX_NM][MAX_NM], AAA[MAX_NM][MAX_NM];
 
inline int num(int i, int j) {
    return (i-)*m + j;
}
 
void mul(ll f[MAX_NM], ll a[MAX_NM][MAX_NM]) {
    ll c[MAX_NM];
    memset(c, , sizeof c);
    for (int j = ; j < MAX_NM; j++)
        for (int k = ; k < MAX_NM; k++)
            c[j] += f[k] * a[k][j];
    memcpy(f, c, sizeof c);
}
 
void mulb(ll a[MAX_NM][MAX_NM], ll b[MAX_NM][MAX_NM]) {
    ll c[MAX_NM][MAX_NM];
    memset(c, , sizeof c);
    for (int i = ; i < MAX_NM; i++)
        for (int j = ; j < MAX_NM; j++)
            for (int k = ; k < MAX_NM; k++)
                c[i][j] += a[i][k]*b[k][j];
    memcpy(a, c, sizeof c);
}
 
void mulself(ll a[MAX_NM][MAX_NM]) {
    ll c[MAX_NM][MAX_NM];
    memset(c, , sizeof c);
    for (int i = ; i < MAX_NM; i++)
        for (int j = ; j < MAX_NM; j++)
            for (int k = ; k < MAX_NM; k++)
                c[i][j] += a[i][k]*a[k][j];
    memcpy(a, c, sizeof c);
}
 
void init()
{
    memset(A, , sizeof A);
    memset(F, , sizeof F);
    F[] = ;
    for (int k = ; k < ; k++) {
        A[k][][] = ;
        for (int i = ; i <= n; i++) {
            for (int j = ; j <= m; j++) {
                int index = opt[i-][j-] - '';
                int indey = k % acts[index].size();
                char ch = acts[index][indey];
 
                if (isupper(ch)) {
                    switch (ch) {
                        case 'N':
                            if (i- >= )
                                A[k][num(i, j)][num(i-, j)] = ; break;
                        case 'S':
                            if (i+ <= n)
                                A[k][num(i, j)][num(i+, j)] = ; break;
                        case 'W':
                            if (j- >= )
                                A[k][num(i, j)][num(i, j-)] = ; break;
                        case 'E':
                            if (j+ <= m)
                                A[k][num(i, j)][num(i, j+)] = ; break;
                        case 'D':
                            A[k][num(i, j)][num(i, j)] = ;
                    }
                }
                if (isdigit(ch)) {
                    A[k][num(i, j)][num(i, j)] = ;
                    A[k][][num(i, j)] = ch - '';
                }
 
            }
        }
    }
    for (int i = ; i < MAX_NM; i++)
        AAA[i][i] = ;
    for (int k = ; k < ; k++)
        mulb(AAA, A[k]);
}
 
int main()
{
    cin >> n >> m >> t >> act;
    for (int i = ; i < n; i++)
        cin >> opt[i];
    for (int i = ; i < act; i++)
        cin >> acts[i];
    init();
    int q = t/;
    int r = t%;
    // t = q*60 + r;
    for (; q; q >>= ) {
        if (q&)
            mul(F, AAA);
        mulself(AAA);
    }
    for (int i = ; i < r; i++)
        mul(F, A[i]);
    ll ans = ;
    for (int i = ; i < MAX_NM; i++)
        ans = max(ans, F[i]);
    cout << ans << endl;
    return ;
}

参考博客：

　　wyboooo's blog