hud 3308 LCIS 线段树 区间合并

题意：

Q a b 查询[a, b]区间的最长连续递增子序列的长度

U a b 将下表为a的元素更新为b

区间合并一般都有3个数组：区间最值，左区间最值和右区间最值

具体详见代码

#include <bits/stdc++.h>
#define lson l, m, rt<<1
#define rson m+1, r, rt<<1|1
using namespace std;

const int MAXN = 111111;
int mx[MAXN<<2], a[MAXN];
int lmx[MAXN<<2], rmx[MAXN<<2];

void push_up(int rt, int l, int r)
{
    lmx[rt] = lmx[rt<<1];
    rmx[rt] = rmx[rt<<1|1];
    mx[rt] = max(mx[rt<<1], mx[rt<<1|1]);
    int m = (l + r) >> 1;
    if(a[m] < a[m+1])   //保证是严格递增的
    {
        if(lmx[rt] == m - l + 1) lmx[rt] += lmx[rt<<1|1];
        if(rmx[rt] == r - m) rmx[rt] += rmx[rt<<1];
        mx[rt] = max(mx[rt], rmx[rt<<1] + lmx[rt<<1|1]);
    }
}

void build(int l, int r, int rt)
{
    if(l == r)
    {
        scanf("%d", &a[l]);
        mx[rt] = lmx[rt] = rmx[rt] = 1;
        return;
    }
    int m = (l + r) >> 1;
    build(lson);
    build(rson);
    push_up(rt, l, r);
}

void update(int p, int c, int l, int r, int rt)
{
    if(l == r)
    {
        a[p] = c;
        return;
    }
    int m = (l + r) >> 1;
    if(m >= p) update(p, c, lson);
    else update(p, c, rson);
    push_up(rt, l, r);
}

int query(int L, int R, int l, int r, int rt)
{
    if(L <= l && r <= R) return mx[rt];
    int m = (l + r) >> 1;
    int ret = 0;
    if(m >= L) ret = max(ret, query(L, R, lson));
    if(m < R) ret = max(ret, query(L, R, rson));
    if(a[m] < a[m+1])   //m-L+1是[L,m]的长度，R-m是[m,R]的长度
        ret = max(ret, min(rmx[rt<<1], m-L+1) + min(lmx[rt<<1|1], R-m));
    return ret;
}

int main()
{
//    freopen("in.txt", "r", stdin);
    int T;
    scanf("%d", &T);
    while(T--)
    {
        int n, m;
        scanf("%d%d", &n, &m);
        build(0, n-1, 1);
        while(m--)
        {
            char op[3];
            int x, y;
            scanf("%s%d%d", op, &x, &y);
            if(op[0] == 'Q') printf("%d\n", query(x, y, 0, n-1, 1));
            else update(x, y, 0, n-1, 1);
        }
    }
    return 0;
}