11<p align =" center " >
2- <a href =" https://mp.weixin.qq.com/s/QVF6upVMSbgvZy8lHZS3CQ " ><img src =" https://img.shields.io/badge/知识星球-代码随想录-blue " alt =" " ></a >
3- <a href =" https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw " ><img src =" https://img.shields.io/badge/刷题-微信群-green " alt =" " ></a >
4- <a href =" https://img-blog.csdnimg.cn/20201210231711160.png " ><img src =" https://img.shields.io/badge/公众号-代码随想录-brightgreen " alt =" " ></a >
5- <a href =" https://space.bilibili.com/525438321 " ><img src =" https://img.shields.io/badge/B站-代码随想录-orange " alt =" " ></a >
6- </p >
7- <p align =" center " ><strong >欢迎大家参与本项目,贡献其他语言版本的代码,拥抱开源,让更多学习算法的小伙伴们收益!</strong ></p >
2+ <a href =" https://mp.weixin.qq.com/s/QVF6upVMSbgvZy8lHZS3CQ " target =" _blank " >
3+ <img src =" https://code-thinking-1253855093.file.myqcloud.com/pics/20210924105952.png " width =" 1000 " />
4+ </a >
5+ <p align =" center " ><strong ><a href =" https://mp.weixin.qq.com/s/tqCxrMEU-ajQumL1i8im9A " >参与本项目</a >,贡献其他语言版本的代码,拥抱开源,让更多学习算法的小伙伴们收益!</strong ></p >
86
97
108## 1. 两数之和
119
12- https://leetcode-cn.com/problems/two-sum/
10+ [ 力扣题目链接 ] ( https://leetcode-cn.com/problems/two-sum/ )
1311
1412给定一个整数数组 nums 和一个目标值 target,请你在该数组中找出和为目标值的那 两个 整数,并返回他们的数组下标。
1513
@@ -29,10 +27,10 @@ https://leetcode-cn.com/problems/two-sum/
2927很明显暴力的解法是两层for循环查找,时间复杂度是O(n^2)。
3028
3129建议大家做这道题目之前,先做一下这两道
32- * [ 242. 有效的字母异位词] ( https://mp.weixin.qq. com/s/vM6OszkM6L1Mx2Ralm9Dig )
33- * [ 349. 两个数组的交集] ( https://mp.weixin.qq. com/s/N9iqAchXreSVW7zXUS4BVA )
30+ * [ 242. 有效的字母异位词] ( https://www.programmercarl. com/0242.有效的字母异位词.html )
31+ * [ 349. 两个数组的交集] ( https://www.programmercarl. com/0349.两个数组的交集.html )
3432
35- [ 242. 有效的字母异位词] ( https://mp.weixin.qq. com/s/vM6OszkM6L1Mx2Ralm9Dig ) 这道题目是用数组作为哈希表来解决哈希问题,[ 349. 两个数组的交集] ( https://mp.weixin.qq. com/s/N9iqAchXreSVW7zXUS4BVA ) 这道题目是通过set作为哈希表来解决哈希问题。
33+ [ 242. 有效的字母异位词] ( https://www.programmercarl. com/0242.有效的字母异位词.html ) 这道题目是用数组作为哈希表来解决哈希问题,[ 349. 两个数组的交集] ( https://www.programmercarl. com/0349.两个数组的交集.html ) 这道题目是通过set作为哈希表来解决哈希问题。
3634
3735本题呢,则要使用map,那么来看一下使用数组和set来做哈希法的局限。
3836
@@ -51,17 +49,18 @@ C++中map,有三种类型:
5149
5250std::unordered_map 底层实现为哈希表,std::map 和std::multimap 的底层实现是红黑树。
5351
54- 同理,std::map 和std::multimap 的key也是有序的(这个问题也经常作为面试题,考察对语言容器底层的理解)。 更多哈希表的理论知识请看[ 关于哈希表,你该了解这些!] ( https://mp.weixin.qq. com/s/g8N6WmoQmsCUw3_BaWxHZA ) 。
52+ 同理,std::map 和std::multimap 的key也是有序的(这个问题也经常作为面试题,考察对语言容器底层的理解)。 更多哈希表的理论知识请看[ 关于哈希表,你该了解这些!] ( https://www.programmercarl. com/哈希表理论基础.html ) 。
5553
5654** 这道题目中并不需要key有序,选择std::unordered_map 效率更高!**
5755
5856解题思路动画如下:
5957
60- <video src =' https://code-thinking.cdn.bcebos.com/gifs/1.%E4%B8%A4%E6%95%B0%E4%B9%8B%E5%92%8C.mp4 ' controls =' controls ' width =' 640 ' height =' 320 ' autoplay =' autoplay ' > Your browser does not support the video tag.</video ></div >
58+ ![ ] ( https://code-thinking.cdn.bcebos.com/gifs/1.两数之和.gif )
59+ 6160
6261C++代码:
6362
64- ``` C++
63+ ``` CPP
6564class Solution {
6665public:
6766 vector<int > twoSum(vector<int >& nums, int target) {
@@ -106,16 +105,17 @@ public int[] twoSum(int[] nums, int target) {
106105
107106Python:
108107
109- ``` python3
108+ ``` python
110109class Solution :
111110 def twoSum (self nums : List[int ], target : int ) -> List[int ]:
112- hashmap= {}
113- for ind,num in enumerate (nums):
114- hashmap[num] = ind
115- for i,num in enumerate (nums):
116- j = hashmap.get(target - num)
117- if j is not None and i!= j:
118- return [i,j]
111+ records = dict ()
112+ 113+ # 用枚举更方便,就不需要通过索引再去取当前位置的值
114+ for idx, val in enumerate (nums):
115+ if target - val not in records:
116+ records[val] = idx
117+ else :
118+ return [records[target - val], idx] # 如果存在就返回字典记录索引和当前索引
119119```
120120
121121
@@ -134,6 +134,21 @@ func twoSum(nums []int, target int) []int {
134134}
135135```
136136
137+ ``` go
138+ // 使用map方式解题,降低时间复杂度
139+ func twoSum (nums []int , target int ) []int {
140+ m := make (map [int ]int )
141+ for index , val := range nums {
142+ if preIndex , ok := m[target-val]; ok {
143+ return []int {preIndex, index}
144+ } else {
145+ m[val] = index
146+ }
147+ }
148+ return []int {}
149+ }
150+ ```
151+ 137152Rust
138153
139154``` rust
@@ -156,11 +171,81 @@ impl Solution {
156171}
157172```
158173
174+ Javascript
159175
176+ ``` javascript
177+ var twoSum = function (nums , target ) {
178+ let hash = {};
179+ for (let i = 0 ; i < nums .length ; i++ ) {
180+ if (hash[target - nums[i]] !== undefined ) {
181+ return [i, hash[target - nums[i]]];
182+ }
183+ hash[nums[i]] = i;
184+ }
185+ return [];
186+ };
187+ ```
160188
189+ php
190+ 191+ ``` php
192+ function twoSum(array $nums, int $target): array
193+ {
194+ for ($i = 0; $i < count($nums);$i++) {
195+ // 计算剩下的数
196+ $residue = $target - $nums[$i];
197+ // 匹配的index,有则返回index, 无则返回false
198+ $match_index = array_search($residue, $nums);
199+ if ($match_index !== false && $match_index != $i) {
200+ return array($i, $match_index);
201+ }
202+ }
203+ return [];
204+ }
205+ ```
206+ 207+ Swift:
208+ ``` swift
209+ func twoSum (_ nums : [Int ], _ target : Int ) -> [Int ] {
210+ var res = [Int ]()
211+ var dict = [Int : Int ]()
212+ for i in 0 ..< nums.count {
213+ let other = target - nums[i]
214+ if dict.keys .contains (other) {
215+ res.append (i)
216+ res.append (dict[other]! )
217+ return res
218+ }
219+ dict[nums[i]] = i
220+ }
221+ return res
222+ }
223+ ```
224+ 225+ PHP:
226+ ``` php
227+ class Solution {
228+ /**
229+ * @param Integer[] $nums
230+ * @param Integer $target
231+ * @return Integer[]
232+ */
233+ function twoSum($nums, $target) {
234+ if (count($nums) == 0) {
235+ return [];
236+ }
237+ $table = [];
238+ for ($i = 0; $i < count($nums); $i++) {
239+ $temp = $target - $nums[$i];
240+ if (isset($table[$temp])) {
241+ return [$table[$temp], $i];
242+ }
243+ $table[$nums[$i]] = $i;
244+ }
245+ return [];
246+ }
247+ }
248+ ```
161249
162250-----------------------
163- * 作者微信:[ 程序员Carl] ( https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw )
164- * B站视频:[ 代码随想录] ( https://space.bilibili.com/525438321 )
165- * 知识星球:[ 代码随想录] ( https://mp.weixin.qq.com/s/QVF6upVMSbgvZy8lHZS3CQ )
166- <div align="center"><img src=../pics/公众号.png width=450 alt=> </img ></div >
251+ <div align="center"><img src=https://code-thinking.cdn.bcebos.com/pics/01二维码一.jpg width=500> </img ></div >
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