题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=3911
此题也是属于线段树的区间合并问题，其实就是一个单纯的区间合并问题，有关线段树区间合并问题，大家可以看一道小编写的更基础的题POJ 3667 Hotel(其实这道题也是蛮基础的)。
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
#define lson l,mid,rt<<1
#define rson mid+1,r,rt<<1|1
const int maxn = 1000000+5;
int wsum[maxn<<2],lwsum[maxn],rwsum[maxn];
int bsum[maxn<<2],lbsum[maxn],rbsum[maxn];
int lazy[maxn];
int num[maxn];
void PushUp(int m,int rt)
{lwsum[rt]=lwsum[rt<<1];lbsum[rt]=lbsum[rt<<1];rwsum[rt]=rwsum[rt<<1|1];rbsum[rt]=rbsum[rt<<1|1];if(lwsum[rt] == m-(m>>1)) lwsum[rt] += lwsum[rt<<1|1];if(lbsum[rt] == m-(m>>1)) lbsum[rt] += lbsum[rt<<1|1];if(rwsum[rt] == (m>>1)) rwsum[rt]+=rwsum[rt<<1];if(rbsum[rt] == (m>>1)) rbsum[rt]+=rbsum[rt<<1];wsum[rt] = max(wsum[rt<<1],wsum[rt<<1|1]);bsum[rt]=max(bsum[rt<<1],bsum[rt<<1|1]);wsum[rt] = max(wsum[rt], rwsum[rt<<1] + lwsum[rt<<1|1]);bsum[rt] = max(bsum[rt], rbsum[rt<<1] + lbsum[rt<<1|1]);
}
void Change(int rt)
{swap(bsum[rt],wsum[rt]);swap(lwsum[rt],lbsum[rt]);swap(rwsum[rt],rbsum[rt]);
}
void PushDown(int rt)
{if(lazy[rt]){lazy[rt<<1]^=1;lazy[rt<<1|1]^=1;lazy[rt]=0;Change(rt<<1);Change(rt<<1|1);}
}
void Build(int l,int r,int rt)
{lazy[rt] = lbsum[rt] = rbsum[rt] = lwsum[rt] = rwsum[rt] = bsum[rt] = wsum[rt]=0;if(l==r){if(num[l]==1) bsum[rt] = lbsum[rt] = rbsum[rt] = 1;else wsum[rt] = lwsum[rt] = rwsum[rt] = 1;return ;}int mid = (l+r)>>1;Build(lson);Build(rson);PushUp(r-l+1,rt);
}
void Update(int L,int R,int l,int r,int rt)
{if(L<=l&&r<=R){lazy[rt]^=1;Change(rt);return ;}PushDown(rt);int mid=(l+r)>>1;if(L<=mid) Update(L,R,lson);if(R>mid) Update(L,R,rson);PushUp(r-l+1,rt);
}
int Query(int L,int R,int l,int r,int rt)
{if(L<=l&&r<=R)return bsum[rt];PushDown(rt);int mid = (l+r)>>1;if( R <= mid ) return Query(L, R, lson);if( L > mid )return Query(L, R, rson);int t1 = Query(L, R, lson);int t2 = Query(L, R, rson);int a = min(mid-L+1, rbsum[rt<<1]);int b = min(R-mid, lbsum[rt<<1|1]);return max(max(t1, t2), a + b);
}
int main(){int n,m,i,j,k,a,b,op;while(scanf("%d",&n)!=EOF){for(i=1;i<=n;i++) scanf("%d",&num[i]);Build(1,n,1);scanf("%d",&m);while(m--){scanf("%d%d%d",&op,&a,&b); if(op==1) Update(a,b,1,n,1);else{int ans=Query(a,b,1,n,1);printf("%d\n",ans);}}}return 0;
}