hdu 1754【I Hate It】

一道简单的线段树题目，好久没有刷题，偶来刷刷，除了刚开始提交RE了，原因是segtree数组开的太小了，一改大就A了，本来代码是用vim写的，用G++编译，结果老是报错，错的都很离谱，就改用code::blocks编译@_@。。。再去研究下G++。。。

#include <cstdio>
#include <algorithm>

const int maxlen = 200000+10;
int scores[maxlen];

struct node
{
    int left,right;
    int value;
    node(){}
    node(int l,int r,int v)
    {
        left = l;
    right = r;
    value = v;
    }
};
node segtree[10*maxlen];

void build(int left,int right,int root)
{
    if(left == right)
    {
    segtree[root] = node(left,right,scores[left]);
    return;
    }

    int mid = (left + right) >> 1;
    int lRoot = root << 1;
    build(left,mid,lRoot);
    build(mid + 1,right,lRoot+1);
    segtree[root] = node(left,right,std::max(segtree[lRoot].value,segtree[lRoot + 1].value));
}

void update(int left,int right,int s,int root,int value)
{
    if(left == right)
    {
    segtree[root].value = value;
    return ;
    }

    int mid = (left + right) >> 1;
    int lRoot = root << 1;
    if(s <= mid)
    {
    update(left,mid,s,lRoot,value);
    segtree[root].value = std::max(segtree[lRoot+1].value,segtree[lRoot].value);
    }
    else
    {
        update(mid + 1,right,s,lRoot + 1,value);
        segtree[root].value = std::max(segtree[lRoot].value,segtree[lRoot+1].value);
    }
}

int query(int left,int right,int root,int l,int r)
{
    if(l == left && r == right)
    {
    return segtree[root].value;
    }

    int mid = (left + right) >> 1;
    int lRoot = root << 1;
    int maxvalue = 0;
    int v;

    if(r <= mid)
    {
    v = query(left,mid,lRoot,l,r);
    maxvalue = std::max(maxvalue,v);
    }else if(l > mid)
    {
    v = query(mid+1,right,lRoot+1,l,r);
    maxvalue = std::max(maxvalue,v);
    }else
    {
    v = query(left,mid,lRoot,l,mid);
    maxvalue = std::max(maxvalue,v);
    v = query(mid+1,right,lRoot+1,mid+1,r);
    maxvalue = std::max(maxvalue,v);
    }

    return maxvalue;
}

int main()
{
    int n,m;

    while(scanf("%d%d",&n,&m) != -1)
    {
    for(int i = 0;i < n;i ++)
    {
        scanf("%d",&scores[i+1]);
    }
            build(1,n,1);

    char str[3];

    for(int i = 0;i < m;i ++)
    {
        scanf("%s",str);
        int a,b;
        scanf("%d%d",&a,&b);
        if(str[0] == 'Q')
        {
        printf("%d\n",query(1,n,1,a,b));
        }else if(str[0] == 'U')
        {
        update(1,n,a,1,b);
        }
    }
    }

    return 0;
}