Leetcode skimming ---1

subject ： Given an array of integers nums  And an integer target value target, Find and in the array as the target value target   the   Two integers , And return their array subscripts . It can be assumed that each input will correspond to only one answer . however , The same element in the array cannot be repeated in the answer . Answers can be returned in any order .

Input ：nums = [2,7,11,15], target = 9

Output ：[0,1]

Method 1 ： Hashtable

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        unordered_map<int, int> hashtable;
        for (int i = 0; i < nums.size(); ++i) {
            auto it = hashtable.find(target - nums[i]);
            if (it != hashtable.end()) {
                return {it -> second, i};
            }
            hashtable[nums[i]] = i;
        }
        return {};
    }
};

Complexity analysis

Time complexity ：O(N)

Spatial complexity ：O(N)