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50 lines
1.1 KiB
Markdown
50 lines
1.1 KiB
Markdown
# [1. Two Sum](https://leetcode.com/problems/two-sum/)
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## 题目
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Given an array of integers, return indices of the two numbers such that they add up to a specific target.
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You may assume that each input would have exactly one solution, and you may not use the same element twice.
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**Example**:
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```
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Given nums = [2, 7, 11, 15], target = 9,
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Because nums[0] + nums[1] = 2 + 7 = 9,
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return [0, 1]
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```
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## 题目大意
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在数组中找到 2 个数之和等于给定值的数字，结果返回 2 个数字在数组中的下标。
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## 解题思路
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这道题最优的做法时间复杂度是 O(n)。
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顺序扫描数组，对每一个元素，在 map 中找能组合给定值的另一半数字，如果找到了，直接返回 2 个数字的下标即可。如果找不到，就把这个数字存入 map 中，等待扫到“另一半”数字的时候，再取出来返回结果。
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## 代码
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```go
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package leetcode
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func twoSum(nums []int, target int) []int {
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m := make(map[int]int)
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for i := 0; i < len(nums); i++ {
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another := target - nums[i]
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if _, ok := m[another]; ok {
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return []int{m[another], i}
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}
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m[nums[i]] = i
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}
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return nil
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}
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``` |