hdu 1754 i hate it（线段树入门）

#include <stdio.h>
#include <string.h>
#define GetMax(a,b) a>b?a:b
#define size 200001
struct seg_tree
{
int left,right;
int max;
}tree[size*4];
int val[size],N,M;
void build(int num,int left,int right)
{
tree[num].left = left;
tree[num].right = right;
if(right-left>1)
{
int mid = (left+right)>>1;
build(2*num,left,mid);
build(2*num+1,mid,right);
tree[num].max = GetMax(tree[2*num].max,tree[2*num+1].max);
}
else
tree[num].max = GetMax(val[left],val[right]);
}
void InputData()
{
int i;
for(i=1;i<=N;i++)
scanf("%d",&val[i]);
scanf("%d",&M);
}
void update(int num,int locate)
{
if (tree[num].right-tree[num].left==1)
{
tree[num].max = GetMax(val[tree[num].right],val[tree[num].left]);
return;
}
int mid = (tree[num].left+tree[num].right)>>1;
if (locate<=mid)
update(2*num,locate);
if(locate>=mid)
update(2*num+1,locate);
tree[num].max = GetMax(tree[2*num].max,tree[2*num+1].max);
}
int query(int num,int left,int right)
{
if(tree[num].left==left&&tree[num].right==right)
return tree[num].max;
int mid = (tree[num].left+tree[num].right)>>1;
if(right<=mid)
return query(2*num,left,right);
else if(left>=mid)
return query(2*num+1,left,right);
else
{
int max1,max2;
max1 = query(2*num,left,mid);
max2 = query(2*num+1,mid,right);
return GetMax(max1,max2);
}
}
int main()
{
char s[2];
int a,b;
while (scanf("%d%d",&N,&M)!=EOF)
{
InputData();
build(1,1,N);
while (M--)
{
scanf("%s%d%d",s,&a,&b);
if (s[0]=='Q')
printf("%d/n",query(1,a,b));
else
val[a] = b,update(1,a);
}
}
return 0;
}