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JavaArithmetic/src/LeetCode/LeetCode167.java at master · freestylewill/JavaArithmetic · GitHub
freestylewill
JavaArithmetic
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src
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LeetCode
/
LeetCode167.java
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JavaArithmetic
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src
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LeetCode
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LeetCode167.java
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package
LeetCode
;
public
class
LeetCode167
{
//https://leetcode.com/problems/two-sum-ii-input-array-is-sorted/description/
/**
* 暴力解法
*
* @param numbers
* @param target
* @return
*/
// 时间复杂度: O(n^2)
// 空间复杂度: O(1)
public
int
[]
twoSum
(
int
[]
numbers
,
int
target
) {
if
(
numbers
.
length
<
2
/*|| !isSorted(numbers)*/
)
throw
new
IllegalArgumentException
(
"Illegal argument numbers"
);
for
(
int
i
=
0
;
i
<
numbers
.
length
;
i
++)
for
(
int
j
=
i
+
1
;
j
<
numbers
.
length
;
j
++)
if
(
numbers
[
i
] +
numbers
[
j
] ==
target
) {
int
[]
res
= {
i
+
1
,
j
+
1
};
return
res
;
}
throw
new
IllegalStateException
(
"The input has no solution"
);
}
// 二分搜索法
// 时间复杂度: O(nlogn)
// 空间复杂度: O(1)
public
int
[]
twoSum2
(
int
[]
numbers
,
int
target
) {
if
(
numbers
.
length
<
2
/*|| !isSorted(numbers)*/
)
throw
new
IllegalArgumentException
(
"Illegal argument numbers"
);
for
(
int
i
=
0
;
i
<
numbers
.
length
-
1
;
i
++) {
int
j
=
binarySearch
(
numbers
,
i
+
1
,
numbers
.
length
-
1
,
target
-
numbers
[
i
]);
if
(
j
!= -
1
) {
// 返回的数从1开始，所以下面都+1了
int
[]
res
= {
i
+
1
,
j
+
1
};
return
res
;
}
}
throw
new
IllegalStateException
(
"The input has no solution"
);
}
private
int
binarySearch
(
int
[]
nums
,
int
l
,
int
r
,
int
target
) {
if
(
l
<
0
||
l
>
nums
.
length
)
throw
new
IllegalArgumentException
(
"l is out of bound"
);
if
(
r
<
0
||
r
>
nums
.
length
)
throw
new
IllegalArgumentException
(
"r is out of bound"
);
while
(
l
<=
r
) {
int
mid
=
l
+ (
r
-
l
) /
2
;
if
(
nums
[
mid
] ==
target
)
return
mid
;
if
(
target
>
nums
[
mid
])
l
=
mid
+
1
;
else
r
=
mid
-
1
;
}
return
-
1
;
}
// 对撞指针
// 时间复杂度: O(n)
// 空间复杂度: O(1)
public
int
[]
twoSum3
(
int
[]
numbers
,
int
target
) {
if
(
numbers
.
length
<
2
/*|| !isSorted(numbers)*/
)
throw
new
IllegalArgumentException
(
"Illegal argument numbers"
);
int
l
=
0
,
r
=
numbers
.
length
-
1
;
while
(
l
<
r
) {
if
(
numbers
[
l
] +
numbers
[
r
] ==
target
) {
int
[]
res
= {
l
+
1
,
r
+
1
};
return
res
;
}
else
if
(
numbers
[
l
] +
numbers
[
r
] <
target
)
l
++;
else
// numbers[l] + numbers[r] > target
r
--;
}
throw
new
IllegalStateException
(
"The input has no solution"
);
}
}
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