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;

}

//