Leetcode1. Two Sum （C++/Python）

最新推荐文章于 2022-02-02 20:32:29 发布

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本文详细解析了一道经典算法题目“两数之和”的高效求解方法，通过使用哈希表来降低时间复杂度，提供了C++和Python两种语言的实现代码。

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Given an array of integers, return indices of the two numbers such that they add up to a specific target.

You may assume that each input would have exactly one solution, and you may not use the same element twice.

Example:

Given nums = [2, 7, 11, 15], target = 9,

Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

解题思路，暴力破解的话，时间复杂度为n^2，可以采用hash思想，边遍历边寻找之前存储的值，使之和为target；以下是hash的解法。

C++版

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        map<int,int>m;
        vector<int>ans;
        for(int i = 0; i < nums.size(); ++ i){
            if(m.find(target-nums[i]) != m.end()){
                ans.push_back(m[target-nums[i]]);
                ans.push_back(i);
                break;
            }
            m[nums[i]] = i;
        }
        return ans;
    }
};

Python版

class Solution(object):
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        List = []
        dic = {}
        for i in range(len(nums)):
            if dic.has_key(target - nums[i]):
                List.append(dic[target - nums[i]])
                List.append(i)
                break
            dic[nums[i]] = i
        return List