POJ 2763 Housewife Wind(树链剖分（边权）)

题意：给你一颗树，树边带权，q次询问，两种操作：

0 u : 求从当前位置到u路径的边权和，（下一次操作时起始位置变成了u）

1 i w : 将第i条边的权值改为w

n < 100001 , q < 100001, w < 10000

思路：还是一个裸的树剖，练练写树剖的熟练度。还有这题貌似卡vector？以后安起见都改用前向星写吧。

代码：

#include<iostream>#include<cstdio>#include<string>#include<cstring>#include<algorithm>using namespace std;typedef long long ll;const int maxn = 1e5+5;int fa[maxn], tree[maxn], son[maxn], deep[maxn], num[maxn], top[maxn], edge_id[maxn];ll treeSum[maxn*4];int k, tot, n, q, s, head[maxn];struct node{    int u, v, w, next;}edge[maxn*2], Edge[maxn*2];void init(){    k = tot = 0;    memset(head, -1, sizeof(head));    memset(son, 0, sizeof(son));    memset(num, 0, sizeof(num));    memset(treeSum, 0, sizeof(treeSum));}void addEdge(int u, int v, int w){    edge[k].v = v;    edge[k].w = w;    edge[k].next = head[u];    head[u] = k++;}void dfs1(int u, int pre, int d){    fa[u] = pre;    deep[u] = d;    num[u] = 1;    for(int i = head[u]; ~i; i = edge[i].next)    {        int v = edge[i].v;        if(v == pre) continue;        dfs1(v, u, d+1);        num[u] += num[v];        if(!son[u] || num[v] > num[son[u]])            son[u] = v;    }}void dfs2(int u, int tp){    tree[u] = tot++;    top[u] = tp;    if(!son[u]) return ;    dfs2(son[u], tp);    for(int i = head[u]; ~i; i = edge[i].next)    {        int v = edge[i].v;        if(v != fa[u] && v != son[u])            dfs2(v, v);    }}void pushup(int root){    treeSum[root] = treeSum[root*2]+treeSum[root*2+1];}void update(int root, int l, int r, int pos, int val){    if(l == r)    {        treeSum[root] = val;        return ;    }    int mid = (l+r)/2;    if(pos <= mid) update(root*2, l, mid, pos, val);    else update(root*2+1, mid+1, r, pos, val);    pushup(root);}ll query(int root, int l, int r, int i, int j){    if(i <= l && j >= r) return treeSum[root];    ll res = 0;    int mid = (l+r)/2;    if(i <= mid) res += query(root*2, l, mid, i, j);    if(j > mid) res += query(root*2+1, mid+1, r, i, j);    return res;}ll cal(int u, int v){    int f1 = top[u], f2= top[v];    ll res = 0;    while(f1 != f2)    {        if(deep[f1] < deep[f2]) swap(f1, f2), swap(u, v);        res += query(1, 1, n, tree[f1], tree[u]);        u = fa[f1];        f1 = top[u];    }    if(u == v) return res;    if(deep[u] > deep[v]) swap(u, v);    res += query(1, 1, n, tree[son[u]], tree[v]);    return res;}int main(void){    while(~scanf("%d%d%d", &n, &q, &s))    {        init();        for(int i = 1; i < n; i++)        {            int u, v, w;            scanf("%d%d%d", &u, &v, &w);            addEdge(u, v, w);            addEdge(v, u, w);            Edge[i] = node{u, v, w};        }        dfs1(1, 0, 1);        dfs2(1, 1);        for(int i = 1; i < n; i++)        {            if(deep[Edge[i].u] > deep[Edge[i].v])                edge_id[i] = Edge[i].u;            else                edge_id[i] = Edge[i].v;        }        for(int i = 1; i < n; i++)            update(1, 1, n, tree[edge_id[i]], Edge[i].w);        while(q--)        {            int cmd, x, y;            scanf("%d%d", &cmd, &x);            if(cmd == 0)            {                printf("%lld\n", cal(s, x));                s = x;            }            else            {                scanf("%d", &y);                update(1, 1, n, tree[edge_id[x]], y);            }        }    }    return 0;}