HDU 1754 I Hate It【线段树】
没想到竟然能一次AC，而且只花了20分钟不到。第一道线段树的题了，纪念一下。
考察线段树的基本操作:建树,区间最值查询和更新操作.
View Code
#include
<
iostream
>
using
namespace
std;
const
int
MAX
=
200005
;
struct
Tree
{
int
left;
int
right;
int
score;
}tr[MAX
*
3
];
int
n,m,s[MAX],a,b;
char
cmd;
int
max(
int
x,
int
y)
{
if
(x
>
y)
return
x;
else
return
y;
}
void
build(
int
l,
int
r,
int
now)
{
tr[now].left
=
l; tr[now].right
=
r;
if
(l
==
r)
{
tr[now].score
=
s[l];
return
;
}
int
mid
=
(l
+
r)
>>
1
;
build(l,mid,(now
<<
1
));
build(mid
+
1
,r,(now
<<
1
)
+
1
);
tr[now].score
=
max(tr[now
<<
1
].score,tr[(now
<<
1
)
+
1
].score);
}
void
modify(
int
l,
int
r,
int
now)
{
if
(l
==
r) { tr[now].score
=
b;
return
; }
int
mid
=
(l
+
r)
>>
1
;
if
(a
<=
mid)
{
modify(l,mid,now
<<
1
);
}
else
if
(a
>
mid)
{
modify(mid
+
1
,r,(now
<<
1
)
+
1
);
}
tr[now].score
=
max(tr[now
<<
1
].score,tr[(now
<<
1
)
+
1
].score);
}
int
query(
int
sta,
int
end,
int
now)
{
if
(tr[now].left
==
sta
&&
tr[now].right
==
end)
return
tr[now].score;
int
mid
=
(tr[now].left
+
tr[now].right)
>>
1
;
if
(end
<=
mid)
{
return
query(sta,end,now
<<
1
);
}
else
if
(sta
>
mid)
{
return
query(sta,end,(now
<<
1
)
+
1
);
}
else
{
int
x
=
query(sta,mid,now
<<
1
);
int
y
=
query(mid
+
1
,end,(now
<<
1
)
+
1
);
return
max(x,y);
}
}
int
main()
{
int
i;
while
(scanf(
"
%d %d
"
,
&
n,
&
m)
!=
EOF)
{
for
(i
=
1
;i
<=
n;
++
i) scanf(
"
%d
"
,
&
s[i]);
build(
0
,n,
1
);
for
(i
=
0
;i
<
m;
++
i)
{
cin
>>
cmd; scanf(
"
%d %d
"
,
&
a,
&
b);
if
(cmd
==
'
Q
'
) printf(
"
%d\n
"
,query(a,b,
1
));
else
modify(
0
,n,
1
);
}
}
return
0
;
}