2525
2626## 解法
2727
28+ 哈希表或双指针实现。时间复杂度均为 ` O(n) ` 。
29+
30+ 哈希表空间复杂度 ` O(n) ` ，双指针则是 ` O(1) ` 。
31+
2832<!-- tabs:start -->
2933
3034### ** Python3**
3135
36+ 哈希表：
37+
38+ ``` python
39+ class Solution :
40+ def twoSum (self nums : List[int ], target : int ) -> List[int ]:
41+ s = set ()
42+ for num in nums:
43+ if target - num in s:
44+ return [num, target - num]
45+ s.add(num)
46+ ```
47+
48+ 双指针：
49+
3250``` python
3351class Solution :
3452 def twoSum (self nums : List[int ], target : int ) -> List[int ]:
@@ -41,31 +59,89 @@ class Solution:
4159 p += 1
4260 else :
4361 q -= 1
44-
4562```
4663
4764### ** Java**
4865
66+ 哈希表：
67+
68+ ``` java
69+ class Solution {
70+ public int [] twoSum (int [] nums , int target ) {
71+ Set<Integer > s = new HashSet<> ();
72+ for (int num : nums) {
73+ if (s. contains(target - num)) {
74+ return new int []{num, target - num};
75+ }
76+ s. add(num);
77+ }
78+ return null ;
79+ }
80+ }
81+ ```
82+
83+ 双指针：
84+
4985``` java
5086class Solution {
5187 public int [] twoSum (int [] nums , int target ) {
52- int p = 0 , q = nums. length - 1 ;
53- while (p < q) {
88+ for (int p = 0 , q = nums. length - 1 ; p < q;) {
5489 int s = nums[p] + nums[q];
5590 if (s == target) {
56- return new int [] {nums[p], nums[q]};
91+ return new int []{nums[p], nums[q]};
5792 }
5893 if (s < target) {
5994 ++ p;
6095 } else {
6196 -- q;
6297 }
6398 }
64- return new int []{ 0 } ;
99+ return null ;
65100 }
66101}
67102```
68103
104+ ### ** C++**
105+
106+ ``` cpp
107+ class Solution {
108+ public:
109+ vector<int > twoSum(vector<int >& nums, int target) {
110+ for (int p = 0, q = nums.size() - 1; p < q;) {
111+ int s = nums[ p] + nums[ q] ;
112+ if (s == target) {
113+ return vector<int >{nums[ p] , nums[ q] };
114+ }
115+ if (s < target) {
116+ ++p;
117+ } else {
118+ --q;
119+ }
120+ }
121+ return vector<int >{};
122+ }
123+ };
124+ ```
125+
126+ ### **Go**
127+
128+ ```go
129+ func twoSum(nums []int, target int) []int {
130+ for p, q := 0, len(nums)-1; p < q; {
131+ s := nums[p] + nums[q]
132+ if s == target {
133+ return []int{nums[p], nums[q]}
134+ }
135+ if s < target {
136+ p++
137+ } else {
138+ q--
139+ }
140+ }
141+ return nil
142+ }
143+ ```
144+
69145### ** JavaScript**
70146
71147``` js
@@ -74,19 +150,18 @@ class Solution {
74150 * @param {number} target
75151 * @return {number[]}
76152 */
77- var twoSum = function (nums , target ) {
78- let left = 0 ;
79- let right = nums . length - 1 ;
80- while (left < right ) {
81- let sum = nums[left] + nums[right ];
82- if (sum === target) {
83- return [nums[left], nums[right]];
84- } else if (sum > target) {
85- right -- ;
86- } else {
87- left ++ ;
153+ var twoSum = function (nums , target ) {
154+ for ( let p = 0 , q = nums . length ; p < q;) {
155+ const s = nums[p] + nums[q] ;
156+ if (s == target ) {
157+ return [ nums[p], nums[q] ];
158+ }
159+ if (s < target) {
160+ ++ p;
161+ } else {
162+ -- q;
163+ }
88164 }
89- }
90165};
91166```
92167
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