Wannafly挑战赛10 D 小H的询问（线段树）

#include <bits/stdc++.h>

using namespace std;

#define rep(i, a, b)	for (int i(a); i <= (b); ++i)
#define dec(i, a, b)	for (int i(a); i >= (b); --i)
#define	ls		i << 1
#define	rs		i << 1 | 1
#define	mid		((l + r) >> 1)
#define	lson		ls, l, mid
#define	rson		rs, mid + 1, r


typedef long long LL;

const int N = 1e5 + 10;

struct node{
	LL c, lc, rc, ret;
	int lo, ro, flag;
} t[N << 2];

int n, m;

void pushup(int i){
	t[i].c = t[ls].c + t[rs].c;
	t[i].ret = max(t[ls].ret, t[rs].ret);
	t[i].flag = 0;
	t[i].lc = t[ls].lc;
	t[i].rc = t[rs].rc;
	t[i].lo = t[ls].lo;
	t[i].ro = t[rs].ro;
	
	if (t[ls].ro ^ t[rs].lo){
		t[i].ret = max(t[i].ret, t[ls].rc + t[rs].lc);
		if (t[ls].flag) t[i].lc = max(t[i].lc, t[ls].c + t[rs].lc);
		if (t[rs].flag) t[i].rc = max(t[i].rc, t[rs].c + t[ls].rc);
		if (t[ls].flag && t[rs].flag) t[i].flag = 1;
	}
}	

void build(int i, int l, int r){
	if (l == r){
		scanf("%lld", &t[i].ret);
		t[i].c = t[i].lc = t[i].rc = t[i].ret;
		t[i].lo = t[i].ro = (t[i].ret & 1);
		t[i].flag = 1;
		return;
	}

	build(lson);
	build(rson);
	pushup(i);
}

void update(int i, int l, int r, int x, LL val){
	if (l == x && l == r){
		t[i].ret = t[i].c = t[i].lc = t[i].rc = val;
		t[i].lo = t[i].ro = (val & 1);
		t[i].flag = 1;
		return;
	}

	if (x <= mid) update(lson, x, val);
	else update(rson, x, val);
	pushup(i);
}

node query(int i, int l, int r, int L, int R){
	if (L <= l && r <= R) return t[i];
	
	if (R <= mid) return query(lson, L, R);
	if (L >  mid) return query(rson, L, R);

	node ta = query(lson, L, mid);
	node tb = query(rson, mid + 1, R);

	node ans;
	ans.c = ta.c + tb.c;
	ans.ret = max(ta.ret, tb.ret);
	ans.flag = 0;
	ans.lc = ta.lc;
	ans.rc = tb.rc;
	ans.lo = ta.lo;
	ans.ro = tb.ro;
	if (ta.ro ^ tb.lo){
		ans.ret = max(ans.ret, ta.rc + tb.lc);
		if (ta.flag) ans.lc = max(ans.lc, ta.c + tb.lc);
		if (tb.flag) ans.rc = max(ans.rc, tb.c + ta.rc);
		if (ta.flag && tb.flag) ans.flag = 1;
	}

	return ans;
}

int main(){

	scanf("%d%d", &n, &m);
	build(1, 1, n);

	while (m--){
		int op;
		scanf("%d", &op);
		if (op == 0){
			int x, y;
			scanf("%d%d", &x, &y);
			node ans = query(1, 1, n, x, y);
			printf("%lld\n", ans.ret);
		}

		else{
			int x;
			LL y;
			scanf("%d%lld", &x, &y);
			update(1, 1, n, x, y);
		}
	}

	return 0;
}