對節點X到Y的最短路上所有點權都加一個數W, 查詢某個點的權值
解 :
這個操作等價於
a. 對X到根節點路徑上所有點權加W
b. 對Y到根節點路徑上所有點權加W
c. 對LCA(x, y)到根節點路徑上所有點權值減W
d. 對LCA(x,y)的父節點 parent(LCA(x, y))到根節點路徑上所有權值減W
於是要進行四次這樣從一個點到根節點的區間修改
將問題進一步簡化, 進行一個點X到根節點的區間修改, 查詢其他一點Y時
只有X在Y的子樹內, X對Y的值才有貢獻且貢獻值為W
於是只需要更新四個點, 查詢一個點的子樹內所有點權的和即可

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

using namespace std;

const int MAXN = 1e5+10;

vector<int> edge[MAXN];
int s[2*MAXN];
int seq[2*MAXN];
int seq1[2*MAXN];
int depth[2*MAXN];
int first[MAXN];
int dp[2*MAXN][25];
int st[MAXN];
int ed[MAXN];
int parent[MAXN];
int cnt, num;

int Lowbit(int x)
{
    return x & (-x);
}

void Add(int x, int val, int n)
{
    if(x <= 0) return;
    for(int i = x; i <= n; i += Lowbit(i)) {
        s[i] += val;
    }
}

int Sum(int x)
{
    int res = 0;
    for(int i = x; i > 0; i -= Lowbit(i)) {
        res += s[i];
    }
    return res;
}

void Dfs(int u, int fa, int dep)
{
    parent[u] = fa;
    seq[++cnt] = u;
    seq1[++num] = u;
    first[u] = num;
    depth[num] = dep;
    st[u] = cnt;
    int len = edge[u].size();
    for(int i = 0; i < len; i++) {
        int v = edge[u][i];
        if(v != fa) {
            Dfs(v, u, dep+1);
            seq1[++num] = u;
            depth[num] = dep;
        }
    }
    seq[++cnt] = u;
    ed[u] = cnt;
}

void RMQ_Init(int n)
{
    for(int i = 1; i <= n; i++) {
        dp[i][0] = i;
    }
    for(int j = 1; (1 << j) <= n; j++) {
        for(int i = 1; i + (1 << j) - 1 <= n; i++) {
            int a = dp[i][j-1], b = dp[i + (1 << (j-1))][j-1];
            dp[i][j] = depth[a] < depth[b] ? a : b;
        }
    }
}

int RMQ_Query(int l, int r)
{
    int k = 0;
    while((1 << (k + 1)) <= r - l + 1) k++;
    int a = dp[l][k], b = dp[r-(1<<k)+1][k];
    return depth[a] < depth[b] ? a : b;
}

int LCA(int u, int v)
{
    int a = first[u], b = first[v];
    if(a > b) a ^= b, b ^= a, a ^= b;
    int res = RMQ_Query(a, b);
    return seq1[res];
}

void Init(int n)
{
    for(int i = 0; i <= n; i++) {
        edge[i].clear();
    }
    memset(s, 0, sizeof(s));
}

int main()
{
    int n, op;
    int u, v, w;
    int cmd;

    while(scanf("%d %d", &n, &op) != EOF) {
        Init(n);
        for(int i = 0; i < n-1; i++) {
            scanf("%d %d", &u, &v);
            edge[u].push_back(v);
            edge[v].push_back(u);
        }
        cnt = 0, num = 0;
        Dfs(1, -1, 0);
        RMQ_Init(num);
        while(op--) {
            scanf("%d", &cmd);
            if(cmd == 0) {
                scanf("%d %d %d", &u, &v, &w);
                int lca = LCA(u, v);
                Add(st[u], w, cnt);
                Add(st[v], w, cnt);
                Add(lca, -w, cnt);
                Add(parent[lca], -w, cnt);
            }
            else if(cmd == 1) {
                scanf("%d", &u);
                printf("%d\n", Sum(ed[u]) - Sum(st[u] - 1));
            }
        }
    }

    return 0;
}