http://www.vijos.cn/Problem_Show.asp?id=1589
这题.....郁闷了首先...
第一眼认为是差分约束系统，可怜的我不会差分....后来在大牛的指点下，明白了一个道理：原来这个题是可以用贪心的哦！
以结束位点先后排序，
用v记录点i是否有西瓜
依次枚举每个条件，
如果范围内的西瓜>=最小西瓜数，则跳过
否则
在没有西瓜的地方填上缺少数量的西瓜（当然尽量往后填，这样可以减少后面的西瓜使用，很好证明的贪心策略！）
当然还要累加使用的西瓜数
于是就这样搞定了........
我汗....不知差分约束系统该怎么写，希望大牛留言补上！先orz.....
如下为在下的AC代码.....
1
Code
2
var
n,m:longint;
3 f:
array
[
0
..
6000
]
of
boolean;
4 c,s,e:
array
[
0
..
3000
]
of
longint;
5
procedure
init;
6
var
i:longint;
7
begin
8 readln(n,m);
9
for
i:
=
1
to
m
do
10
begin
11 readln(s[i],e[i],c[i]);
12
end
;
13
end
;
14
procedure
qsort(l,r:longint);
15
var
i,j,x,t:Longint;
16
begin
17 i:
=
l;j:
=
r;
18 x:
=
e[(i
+
j) shr
1
];
19
repeat
20
while
e[i]
<
x
do
inc(i);
21
while
e[j]
>
x
do
dec(j);
22
if
i
<=
j
then
23
begin
24 t:
=
e[i];e[i]:
=
e[j];e[j]:
=
t;
25 t:
=
s[i];s[i]:
=
s[j];s[j]:
=
t;
26 t:
=
c[i];c[i]:
=
c[j];c[j]:
=
t;
27 inc(i);dec(j);
28
end
;
29
until
i
>
j;
30
if
l
<
j
then
qsort(l,j);
31
if
i
<
r
then
qsort(i,r);
32
end
;
33
procedure
find;
34
var
i,j,sum,ans:longint;
35
begin
36 fillchar(f,sizeof(f),
0
);
37 ans:
=
0
;
38
for
i:
=
1
to
m
do
39
begin
40 sum:
=
0
;
41
for
j:
=
s[i]
to
e[i]
do
if
f[j]
then
inc(sum);
42
if
sum
>=
c[i]
then
continue;
43 sum:
=
c[i]
-
sum;
44 ans:
=
ans
+
sum;
45
for
j:
=
e[i]
downto
s[i]
do
46
begin
47
if
not
(f[j])
then
48
begin
49 dec(sum);
50 f[j]:
=
true;
51
if
sum
=
0
then
break;
52
end
;
53
end
;
54
end
;
55 writeln(ans);
56
end
;
57
begin
58 init;
59 qsort(
1
,m);
60 find;
61
end
.
Code2
var
n,m:longint;3
f:
array
[
0
..
6000
]
of
boolean;4
c,s,e:
array
[
0
..
3000
]
of
longint;5
procedure
init;6
var
i:longint;7
begin
8
readln(n,m);9
for
i:
=
1
to
m
do
10
begin
11
readln(s[i],e[i],c[i]);12
end
; 13
end
;14
procedure
qsort(l,r:longint);15
var
i,j,x,t:Longint;16
begin
17
i:
=
l;j:
=
r;18
x:
=
e[(i
+
j) shr
1
];19
repeat
20
while
e[i]
<
x
do
inc(i);21
while
e[j]
>
x
do
dec(j);22
if
i
<=
j
then
23
begin
24
t:
=
e[i];e[i]:
=
e[j];e[j]:
=
t;25
t:
=
s[i];s[i]:
=
s[j];s[j]:
=
t;26
t:
=
c[i];c[i]:
=
c[j];c[j]:
=
t;27
inc(i);dec(j);28
end
;29
until
i
>
j;30
if
l
<
j
then
qsort(l,j);31
if
i
<
r
then
qsort(i,r);32
end
;33
procedure
find;34
var
i,j,sum,ans:longint;35
begin
36
fillchar(f,sizeof(f),
0
);37
ans:
=
0
;38
for
i:
=
1
to
m
do
39
begin
40
sum:
=
0
;41
for
j:
=
s[i]
to
e[i]
do
if
f[j]
then
inc(sum);42
if
sum
>=
c[i]
then
continue;43
sum:
=
c[i]
-
sum;44
ans:
=
ans
+
sum;45
for
j:
=
e[i]
downto
s[i]
do
46
begin
47
if
not
(f[j])
then
48
begin
49
dec(sum);50
f[j]:
=
true;51
if
sum
=
0
then
break;52
end
;53
end
;54
end
;55
writeln(ans);56
end
;57
begin
58
init;59
qsort(
1
,m);60
find;61
end
.
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