HDOJ 1754 I Hate It

线段树入门题，和敌兵布阵一样只有更新和查询操作，维护的是最大值；

# include <stdio.h>
# include <string.h>

# define N (1 << 19)
# define M (1 << 18)

int segMax[N*2+10];

int max(int x, int y)
{
    return x>y ? x:y;
}

void initTree(void)
{
    segMax[0] = 0;

    memset(segMax, 0, sizeof(segMax));
}

int update(int p, int val)
{
    p += M;

    segMax[p] = val;
    while (segMax[p >>= 1] < val)
    {
        segMax[p] = val;
    }
}

int query(int s, int t)
{
    int ret;

    ret = 0;
    s += M-1, t += M+1;
    while ((s^t) != 1)
    {
        if ((s&0x1) == 0) ret = max(ret, segMax[s+1]);
        if ((t&0x1) == 1) ret = max(ret, segMax[t-1]);
        s >>= 1, t >>= 1;
    }

    return ret;
}

int main()
{
    char ch[5];
    int n, m, i, tmp, x, y;

    while (~scanf("%d%d", &n, &m))
    {
        initTree();
        for (i = 1; i <= n; ++i)
        {
            scanf("%d", &tmp);
            update(i, tmp);
        }
        for (i = 0; i < m; ++i)
        {
            scanf("%s%d%d", &ch, &x, &y);
            if (ch[0] == 'Q')
            {
                if (x > y) tmp = x, x = y, y = tmp;
                printf("%d\n", query(x, y));
            }
            else if (ch[0] == 'U') update(x, y);
        }
    }

    return 0;
}

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