OJ-Problems-Source/HDOJ/1754.cpp
2016-08-17 11:00:49 +08:00

115 lines
2.7 KiB
C++

/// General includes
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <algorithm>
using namespace std;
/// 最基础的线段树: 单点更新,区间运算(求和)
namespace SegmentTree
{
const int MAXN = 1000100;
const int MAXTREENODE = MAXN<<2;
struct node
{
int lt,rt;
int val;
};
node tree[MAXTREENODE];
/// _internal_v is a indexer of SegmentTree. It guides the procedure to the right node.
void build(int L,int R,int _internal_v=1) /// Build a tree, _internal_v is 1 by default.
{
tree[_internal_v].lt=L;
tree[_internal_v].rt=R;
if(L==R)
{
scanf("%d",&tree[_internal_v].val);
/// Or: tree[_internal].val = VAL_BY_DEFAULT
return;
}
int mid=(L+R)>>1;
build(L,mid,_internal_v<<1);
build(mid+1,R,_internal_v<<1|1);/// x<<1 == x*2; x<<1|1 == x*2+1; (faster == slower)
/// SegmentTree Main Algorithm
tree[_internal_v].val=max(tree[_internal_v<<1].val,tree[_internal_v<<1|1].val);
}
void update(int Pos,int Val,int _internal_v=1)/// Update a position, _internal_v is 1 by default.
{
if(tree[_internal_v].lt==tree[_internal_v].rt)
{
tree[_internal_v].val=Val;
return;
}
/// Update Deep-Loop
if(Pos <= tree[_internal_v<<1].rt) update(Pos,Val,_internal_v<<1);
if(Pos >= tree[_internal_v<<1|1].lt) update(Pos,Val,_internal_v<<1|1);
/// SegmentTree Main Algorithm
tree[_internal_v].val = max(tree[_internal_v<<1].val,tree[_internal_v<<1|1].val);
}
int _internal_ans;
inline void _internal_clear_ans()
{
_internal_ans=0;
}
inline int _internal_get_ans()
{
return _internal_ans;
}
void basic_query(int L,int R,int _internal_v=1)/// Query A Segment [L,R] , _internal_v is 1 by default.
{
if(tree[_internal_v].lt >= L && tree[_internal_v].rt <= R)
{
_internal_ans=max(_internal_ans,tree[_internal_v].val);
return;
}
if(L <= tree[_internal_v<<1].rt) basic_query(L,R,_internal_v<<1);
if(R >= tree[_internal_v<<1|1].lt) basic_query(L,R,_internal_v<<1|1);
}
int query(int L,int R)
{
_internal_clear_ans();
basic_query(L,R);
return _internal_get_ans();
}
}/// End of namespace SegmentTree
char str[8];
int main()
{
using namespace SegmentTree;
int n,q;
while(scanf("%d %d",&n,&q)==2)
{
build(1,n);
for(int i=0; i<q; i++)
{
int a,b;
scanf("%s %d %d",str,&a,&b);
switch(str[0])
{
case 'Q':
{
int ans=query(a,b);
printf("%d\n",ans);
}
break;
case 'U':
{
update(a,b);
}
}
}
}
return 0;
}