#include
<iostream>
using

namespace

std
;
#include
<vector>
void

merge
(vector
<
int
>&
a,
int
low,
int
middle,
int
high)
{
vector
<
int
>
b;
//辅助数组

for
(
int
i
=
0
;i
<
a.
size
();i
++
)
b.
push_back
(a[i]);

int
index1,index2,k;

for
( index1
=
low,index2
=
middle
+
1
,k
=
low; index1
<=
middle
&&
index2
<=
high; k
++
)
//i j是B的指针
{

if
(b[index1]
<
b[index2])
a[k]
=
b[index1
++
];

else
a[k]
=
b[index2
++
];
}

//只能执行一句

while
(index1
<=
middle) a[k
++
]
=
b[index1
++
];

while
(index2
<=
middle) a[k
++
]
=
b[index2
++
];
}
void

MergeSort
(vector
<
int
>&
a,
int
low,
int
high)
{

if
(low
<
high)
{

int
middle
=
(low
+
high)
/
2
;

MergeSort
(a,low,middle
–
1
);

MergeSort
(a,middle
+
1
,high);

merge
(a,low,middle,high);
}
}

int

main
()
{
vector
<
int
>
a;

int
length;
std::cout
<<
“input the length :”
<<
endl;
std::cin
>>
length;

for
(
int
i
=
0
;i
<
length;i
++
)
{

int
temp;
std::cin
>>
temp;
a.
push_back
(temp);
}

MergeSort
(a,
0
,length
–
1
);

cout
<<
“output a: “
<<
endl;

for
(
int
i
=
0
;i
<
length;i
++
)
std::cout
<<
a[i]
<<
” “
<<
endl;
}
/*归并排序法：
T(n)=nlogn
空间复杂度：O(n)
*/