版权声明：https://blog.csdn.net/qq_41730082 https://blog.csdn.net/qq_41730082/article/details/85858378
题目链接
这道题，说来还的确困扰了我一个多小时，当时就在想，我该如何处理那些边权（我将边化为点）以及点（默认权值为0）的取相反数后的处理（因为点取相反数之后还是0），会困扰到那些边的。
然后，我想到了，如果这段区间的返回的值为0，那么就说明了肯定是点的，我们不妨返回的是(-INF)即可。然后，再pushup()的时候，也做了相似的处理，毕竟，两点之间确定一条边，所以，我们线段树的操作的时候，如果，左儿子或者右儿子为0，我们取另外一头，绝对是可以的，于是，就这样子敲了，A了！
最后，附上一组测试数组，那个“-48”过了，基本问题不大（我就是一直卡在“-48”），过了，就没其他问题了。
#include <iostream>
#include <cstdio>
#include <cmath>
#include <string>
#include <cstring>
#include <algorithm>
#include <limits>
#include <vector>
#include <stack>
#include <queue>
#include <set>
#include <map>
#define lowbit(x) ( x&(-x) )
#define pi 3.141592653589793
#define e 2.718281828459045
#define INF 40000007
using namespace std;
typedef unsigned long long ull;
typedef long long ll;
const int maxN = 20005;
int N, all_point, W[maxN], cnt, head[maxN], deep[maxN], root[maxN], siz[maxN], W_son[maxN], top[maxN], id[maxN], new_W[maxN], num, tree[maxN<<2], minn[maxN<<2], lazy[maxN<<2];
struct Eddge
{
int nex, to;
Eddge(int a=-1, int b=0):nex(a), to(b) {}
}edge[maxN<<1];
void addEddge(int u, int v)
{
edge[cnt] = Eddge(head[u], v);
head[u] = cnt++;
}
inline void dfs1(int u, int fa, int depth)
{
root[u] = fa;
deep[u] = depth;
siz[u] = 1;
int Minn = -1;
for(int i=head[u]; i!=-1; i=edge[i].nex)
{
int v = edge[i].to;
if(v == fa) continue;
dfs1(v, u, depth+1);
siz[u] += siz[v];
if(siz[v] > Minn)
{
Minn = siz[v];
W_son[u] = v;
}
}
}
inline void dfs2(int u, int topf)
{
top[u] = topf;
id[u] = ++num;
new_W[num] = W[u];
if(W_son[u] == 0) return;
dfs2(W_son[u], topf);
for(int i=head[u]; i!=-1; i=edge[i].nex)
{
int v = edge[i].to;
if(v == root[u] || v == W_son[u]) continue;
dfs2(v, v);
}
}
void pushup(int rt)
{
if(tree[rt<<1] == 0)
{
tree[rt] = tree[rt<<1|1];
minn[rt] = minn[rt<<1|1];
return;
}
if(tree[rt<<1|1] == 0)
{
tree[rt] = tree[rt<<1];
minn[rt] = minn[rt<<1];
return;
}
tree[rt] = max(tree[rt<<1], tree[rt<<1|1]);
minn[rt] = min(minn[rt<<1], minn[rt<<1|1]);
}
inline void buildTree(int rt, int l, int r)
{
lazy[rt] = 0;
if(l == r)
{
tree[rt] = minn[rt] = new_W[l];
return;
}
int mid = (l + r)>>1;
buildTree(rt<<1, l, mid);
buildTree(rt<<1|1, mid+1, r);
pushup(rt);
}
void pushdown(int rt)
{
if(lazy[rt])
{
lazy[rt<<1] ^= 1;
lazy[rt<<1|1] ^= 1;
int t1 = tree[rt<<1], t2 = tree[rt<<1|1];
tree[rt<<1] = -minn[rt<<1];
minn[rt<<1] = -t1;
tree[rt<<1|1] = -minn[rt<<1|1];
minn[rt<<1|1] = -t2;
lazy[rt] = 0;
}
}
void update_1(int rt, int l, int r, int qx, int val)
{
if(l == r)
{
tree[rt] = minn[rt] = val;
return;
}
pushdown(rt);
int mid = (l + r)>>1;
if(qx<=mid) update_1(rt<<1, l, mid, qx, val);
else update_1(rt<<1|1, mid+1, r, qx, val);
pushup(rt);
}
void update_2(int rt, int l, int r, int ql, int qr)
{
if(ql<=l && qr>=r)
{
lazy[rt] ^= 1;
int tmp = tree[rt];
tree[rt] = -minn[rt];
minn[rt] = -tmp;
return;
}
pushdown(rt);
int mid = (l + r)>>1;
if(ql>mid) update_2(rt<<1|1, mid+1, r, ql, qr);
else if(qr<=mid) update_2(rt<<1, l, mid, ql, qr);
else
{
update_2(rt<<1, l, mid, ql, qr);
update_2(rt<<1|1, mid+1, r, ql, qr);
}
pushup(rt);
}
void change_line(int pos, int val) { update_1(1, 1, all_point, id[pos + N], val); }
void Negate_line(int x, int y)
{
while(top[x] != top[y])
{
if(deep[top[x]] < deep[top[y]]) swap(x, y);
update_2(1, 1, all_point, id[top[x]], id[x]);
x = root[top[x]];
}
if(deep[x] > deep[y]) swap(x, y);
update_2(1, 1, all_point, id[x], id[y]);
}
int query(int rt, int l, int r, int ql, int qr)
{
if(ql<=l && qr>=r) return tree[rt] == 0?(-INF):tree[rt];
pushdown(rt);
int mid = (l + r)>>1;
if(ql > mid) return query(rt<<1|1, mid+1, r, ql, qr);
else if(qr <= mid) return query(rt<<1, l, mid, ql, qr);
else return max(query(rt<<1, l, mid, ql, qr), query(rt<<1|1, mid+1, r, ql, qr));
}
int query_range(int x, int y)
{
int ans = -INF;
while(top[x] != top[y])
{
if(deep[top[x]] < deep[top[y]]) swap(x, y);
ans = max(ans, query(1, 1, all_point, id[top[x]], id[x]));
x = root[top[x]];
}
if(deep[x] > deep[y]) swap(x, y);
ans = max(ans, query(1, 1, all_point, id[x], id[y]));
return ans;
}
inline void init()
{
cnt = num = 0;
memset(W, 0, sizeof(W));
memset(W_son, 0, sizeof(W_son));
memset(head, -1, sizeof(head));
}
char op[10];
int main()
{
int T; scanf("%d", &T);
while(T--)
{
init();
scanf("%d", &N);
all_point = N;
for(int i=1; i<N; i++)
{
int e1, e2, e3;
scanf("%d%d%d", &e1, &e2, &e3);
W[++all_point] = e3;
addEddge(e1, all_point);
addEddge(all_point, e1);
addEddge(all_point, e2);
addEddge(e2, all_point);
}
dfs1(1, 1, 0);
dfs2(1, 1);
buildTree(1, 1, all_point);
while(scanf("%s", op) && op[0] != 'D')
{
int e1, e2;
scanf("%d%d", &e1, &e2);
if(op[0] == 'C') change_line(e1, e2);
else if(op[0] == 'N') Negate_line(e1, e2);
else printf("%d\n", query_range(e1, e2));
}
}
return 0;
}
/*
1
15
7 1 93
6 2 41
6 1 48
14 4 62
12 15 43
7 8 2
2 10 80
7 13 92
13 5 91
13 11 5
15 1 79
2 3 21
9 12 7
15 4 33
Q 13 7
C 6 6
N 13 1
Q 3 15
C 12 11
N 14 11
Q 2 11
N 2 7
Q 6 7
C 11 10
N 3 8
Q 14 8
C 3 4
Q 8 13
C 5 1
N 7 1
Q 1 11
C 11 8
DONE
ans:
> 92
> 79
> 93
> -48
> 93
> 92
> 92
*/