Tree Generator™ CodeForces - 1149C (线段树,括号序列)

大意: 给定括号序列, 每次询问交换两个括号, 求括号树的直径.

用[ZJOI2007]捉迷藏的方法维护即可.

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <queue>
#define REP(i,a,n) for(int i=a;i<=n;++i)
#define pb push_back
#define lc (o<<1)
#define rc (lc|1)
#define mid ((l+r)>>1)
#define ls lc,l,mid
#define rs rc,mid+1,r
using namespace std;
const int N = 3e5+10, INF = 0x3f3f3f3f;
int n, m;
char s[N];

struct _ {
	int l,r,dis,l_plus,l_minus,r_plus,r_minus;
	_ (int l=0,int r=0,int dis=0,int l_plus=0,int l_minus=0,int r_plus=0,int r_minus=0) : l(l),r(r),dis(dis),l_plus(l_plus),l_minus(l_minus),r_plus(r_plus),r_minus(r_minus) {}
	_ operator + (const _ &rhs) const {
		_ ret;
		ret.l = l+max(rhs.l-r,0);
		ret.r = rhs.r+max(r-rhs.l,0);
		ret.l_plus = max({l_plus,l+r+rhs.l_minus,l-r+rhs.l_plus});
		ret.l_minus = max(l_minus,rhs.l_minus+r-l);
		ret.r_plus = max({rhs.r_plus,r_plus-rhs.l+rhs.r,r_minus+rhs.l+rhs.r});
		ret.r_minus = max(rhs.r_minus,r_minus+rhs.l-rhs.r);
		ret.dis = max({dis,rhs.dis,r_plus+rhs.l_minus,r_minus+rhs.l_plus});
		return ret;
	}
} tr[N<<2];

void build(int o, int l, int r) {
	if (l==r) tr[o]=_(s[l]==')',s[l]=='(');
	else build(ls),build(rs),tr[o]=tr[lc]+tr[rc];
}
void update(int o, int l, int r, int x) {
	if (l==r) {
		if (s[l]=='(') s[l]=')',tr[o]=_(1,0);
		else s[l]='(',tr[o]=_(0,1);
	}
	else mid>=x?update(ls,x):update(rs,x),tr[o]=tr[lc]+tr[rc];
}
int main() {
	scanf("%d%d%s", &n, &m, s+1);
	n <<= 1;
	build(1,1,n);
	printf("%d\n", tr[1].dis);
	while (m--) {
		int x, y;
		scanf("%d%d", &x, &y);
		update(1,1,n,x);
		update(1,1,n,y);
		printf("%d\n", tr[1].dis);
	}
}