HDU_1754_线段树

题意：区间最值问题，线段树模板水题：

#include <cstdio>
#include <cstring>

using namespace std;

const int N = 200000 + 10;

int maxnumb[N<<2];

int MAX(int a, int b)
{
    return a<b ? b : a;
}

void build(int l, int r, int rt)
{
	if(l == r)
	{
		scanf("%d", &maxnumb[rt]);
		return ;
	}

	int m = (l+r) >> 1, rtt = rt << 1;
	build(l, m, rtt);
	build(m+1, r, rtt+1);
	maxnumb[rt] = MAX(maxnumb[rtt], maxnumb[rtt+1]);
}

void update(int p, int add, int l, int r, int rt)
{
	if(l == r)
	{
		maxnumb[rt] = add;
		return ;
	}

	int m = (l+r) >> 1, rtt = rt << 1;
	if(p <= m)	update(p, add, l, m, rtt);
	else		update(p, add, m+1, r, rtt+1);
	maxnumb[rt] = MAX(maxnumb[rtt], maxnumb[rtt+1]);
}

int query(int L, int R, int l, int r, int rt)
{
	if(L<=l && R>=r)
	{
		return maxnumb[rt];
	}

	int m = (l+r) >> 1, rtt = rt << 1, ans = 0;
	if(L <= m)	ans = MAX(query(L, R, l, m, rtt), ans);
	if(R > m)	ans = MAX(query(L, R, m+1, r, rtt+1), ans);

	return ans;
}

int main()
{
    int n, m, a, b;
    while(~scanf("%d%d", &n, &m))
    {
        memset(maxnumb, 0, sizeof(maxnumb));
        build(1, n, 1);

        char ch;
        for(int i=0; i<m; ++i)
        {
            getchar();
            scanf("%c", &ch);

            if(ch == 'Q') scanf("%d%d", &a, &b), printf("%d\n", query(a, b, 1, n, 1));
            if(ch == 'U') scanf("%d%d", &a, &b), update(a, b, 1, n, 1);
        }
    }

	return 0;
}