LeetCode-001 Two Sum
2017-09-10 20:56
393 查看
Description
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].
Analyse
其实这道题看起来很简单,就是在一个集合里面找到两个和为目标值的下标,只要学过一些基础的人都很容易想到时间复杂度为O(n2)的算法,就是两个循环遍历整个集合即可。这道题到这里就结束了,这就是这道题被评为Easy的原因。其实还有更快的,我们可以想到,若将集合先排好序,然后再去查找,时间复杂度将会降到O(nlogn)。要是再快点的话,直接做哈希,将每个元素做哈希,然后遍历整个集合,将目标值减去遍历值的差做哈希,哈希到的就是答案(因为题目保证了答案的唯一性),时间复杂度为O(n),但空间复杂度也随之变大。
Code
这里只列出最简单的方法吧class Solution { public: vector<int> twoSum(vector<int>& nums, int target) { vector<int> ans; for (int i=0;i<nums.size()-1;i++) { for (int j=i+1;j<nums.size();j++) { if (nums[i]+nums[j]==target) { ans.push_back(i); ans.push_back(j); return ans; } } } } };
相关文章推荐
- 2017-09-07 LeetCode_001 Two Sum
- LeetCode 001-Two Sum
- 001_LeetCode_1 Two Sum 题解
- [Leetcode题解]001 Two Sum
- 【LeetCode】 001. Two Sum
- leetcode001 Two Sum
- LeetCode 001 Two Sum
- 【JAVA、C++】LeetCode 001 Two Sum
- leetcode-001-Two sum
- LeetCode 001 Two Sum
- [LeetCode 001] Two Sum
- leetcode [001] : Two Sum
- LeetCode001__TWO SUM
- [LeetCode]-001-Two Sum
- LeetCode 001 Two Sum
- leetcode_001 two sum
- 【LeetCode】001.Two Sum
- LeetCode 001 :Two Sum
- leetcode001——Two Sum
- 【leetcode 001】Two Sum || Add Two Numbers