HDU 1754 I Hate It

同样是线段树，这道题是求区间最值，单点更新。线段树代码愈发熟练。

/*2012-08-07 16:02:53    Accepted    1754    1093MS    2276K    1361 B    G++    Yu*/
#include<stdio.h>
#include<algorithm>
using namespace std;
#define lson l, m, rt << 1
#define rson m + 1, r, rt << 1 | 1

const int MAXN = 200020;
int Max[MAXN << 2];
int n, m;

void PushUp(int rt)
{
    Max[rt] = max(Max[rt << 1], Max[rt << 1 | 1]);
}

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

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

int query(int L, int R, int l, int r, int rt)
{
    int ret = 0, m = l + r >> 1;
    if(L <= l && r <= R)
    {
        return Max[rt];
    }
    if(L <= m) ret = max(ret, query(L, R, lson));
    if(R > m) ret = max(ret, query(L, R, rson));
    return ret;
}

void operation()
{
    char op[5];
    int a, b;
    while(m --)
    {
        scanf("%s%d%d", op, &a, &b);
        if('Q' == op[0])
            printf("%d\n", query(a, b, 1, n, 1));
        else
            update(a, b, 1, n, 1);
    }
}

int main()
{
    while(scanf("%d%d", &n, &m) == 2)
    {
        build(1, n, 1);
        operation();
    }
    return 0;
}