洛谷 #3384. 树链剖分

题意

树上区间修改、查询

题解

树链剖分+线段树

调试记录

线段树update没有pushdown

没有遍历重儿子

size没有跟新

dep大的dfn小

#include <cstdio>
#include <algorithm>
#define maxn 100005

using namespace std;

struct node{
	int to, next;
}e[maxn << 1];

int head[maxn], n, m, root, mo, val[maxn], val2[maxn];
int f[maxn], dep[maxn], dfn[maxn], size[maxn], son[maxn], top[maxn];

struct node2{
	int key, l, r, lazy;
}a[maxn << 2];

int tot = 0;
void addedge(int u, int v){
	e[++tot] = (node){v, head[u]}; head[u] = tot;
}

int cnt = 0;
void dfs(int cur, int fa, int deep){
	f[cur] = fa;
	dep[cur] = deep;
	size[cur] = 1;
	
	int Max = -1;
	for (int i = head[cur]; i; i = e[i].next){
		if (e[i].to != fa){
			dfs(e[i].to, cur, deep + 1);
			size[cur] += size[e[i].to];
			if (size[e[i].to] > Max) Max = size[e[i].to], son[cur] = e[i].to;
		}
	}
}

void dfs2(int cur, int topf){
	top[cur] = topf;
	dfn[cur] = ++cnt;
	val2[cnt] = val[cur];
	if (!son[cur]) return;
	
	dfs2(son[cur], topf);
	for (int i = head[cur]; i; i = e[i].next){
		if (e[i].to != f[cur] && e[i].to != son[cur]){
			dfs2(e[i].to, e[i].to);
		}
	}
}

void pushdown(int cur){
	if (!a[cur].lazy) return;
	int mid = (a[cur].l + a[cur].r) >> 1;
	(a[cur << 1].key += (a[cur].lazy * (mid - a[cur].l + 1))) %= mo;
	(a[cur << 1 | 1].key += (a[cur].lazy * (a[cur].r - mid))) %= mo;
	(a[cur << 1].lazy += a[cur].lazy) %= mo;
	(a[cur << 1 | 1].lazy += a[cur].lazy) %= mo;
	a[cur].lazy = 0;
}

void update(int cur, int l, int r, int k){
	if (a[cur].l > r || a[cur].r < l) return;
	if (a[cur].l >= l && a[cur].r <= r){
		(a[cur].key += (a[cur].r - a[cur].l + 1) * k) %= mo;
		(a[cur].lazy += k) %= mo;
		return;
	}
	
	pushdown(cur);
	int mid = (a[cur].l + a[cur].r) >> 1;
	update(cur << 1, l, r, k);
	update(cur << 1 | 1, l, r, k);
	a[cur].key = (a[cur << 1].key + a[cur << 1 | 1].key) % mo;
}

void build(int cur, int l, int r){
	a[cur].l = l, a[cur].r = r;
	
	if (l == r){
		a[cur].key = val2[l] % mo;
		return;
	}
	
	int mid = (l + r) >> 1;
	build(cur << 1, l, mid);
	build(cur << 1 | 1, mid + 1, r);
	a[cur].key = (a[cur << 1].key + a[cur << 1 | 1].key) % mo;
}

int Query(int cur, int l, int r){
	if (a[cur].l > r || a[cur].r < l) return 0;
	if (a[cur].l >= l && a[cur].r <= r) return a[cur].key;
	
	pushdown(cur);
	return (Query(cur << 1, l, r) + Query(cur << 1 | 1, l, r)) % mo;
}

int qRange(int x, int y){
	int ans = 0;
	while (top[x] != top[y]){
		if (dep[top[x]] < dep[top[y]]) swap(x, y);
		(ans += Query(1, dfn[top[x]], dfn[x])) %= mo;
		x = f[top[x]];
	}
	
	if (dep[x] > dep[y]) swap(x, y);
	(ans += Query(1, dfn[x], dfn[y])) %= mo;
	return ans;
}

void uRange(int x, int y, int k){
	k %= mo;
	while (top[x] != top[y]){
		if (dep[top[x]] < dep[top[y]]) swap(x, y);
		update(1, dfn[top[x]], dfn[x], k);
		x = f[top[x]];
	}
	
	if (dep[x] > dep[y]) swap(x, y);
	update(1, dfn[x], dfn[y], k);
}

int qSon(int x){
	return Query(1, dfn[x], dfn[x] + size[x] - 1);
}

void uSon(int x, int k){
	update(1, dfn[x], dfn[x] + size[x] - 1, k);
}

inline int read(){
	int x = 0; char ch = getchar();
	while (ch < '0' || ch > '9') ch = getchar();
	while (ch >= '0' && ch <= '9') x = x * 10 + (ch - '0'), ch = getchar();
	return x;
}

int main(){
	n = read(), m = read(), root = read(), mo = read();
	for (int i = 1; i <= n; i++) val[i] = read();
	for (int x, y, i = 1; i < n; i++){
		x = read(), y = read(); addedge(x, y); addedge(y, x);
	}
	
	dfs(root, 0, 1);
	dfs2(root, root);
	build(1, 1, n);
	
	for (int opt, x, y, k, i = 1; i <= m; i++){
		opt = read();
		
		if (opt == 1){
			x = read(), y = read(), k = read();
			uRange(x, y, k);
		}
		if (opt == 2){
			x = read(), y = read();
			printf("%d\n", qRange(x, y));
		}
		if (opt == 3){
			x = read(), k = read();
			uSon(x, k);
		}
		if (opt == 4){
			x = read();
			printf("%d\n", qSon(x));
		}
	}
	
	return 0;
}