[LeetCode | C++] August LeetCoding Challenge 2021 — Week1 Two Sum (2nd, August)

📃 Problem

https://leetcode.com/explore/challenge/card/august-leetcoding-challenge-2021/613/week-1-august-1st-august-7th/3836/

💡 Check Point

• Consider how to get the index of a given value in vector “nums”

👩‍💻 My Solution

1. First Approach — Implementation

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        vector<int> result;
        
        for(int i = 0 ; i <nums.size(); i++) {
            for(int j = i+1; j < nums.size(); j++) {
                if(i == j) continue;
                
                if(nums[i]+nums[j] == target) {
                    result.push_back(i);
                    result.push_back(j);
                    
                    break;
                }
            }
        }
        
        return result;
    }
};

2. Second Approach — Using “find” method of vector

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        vector<int> result;
        
        for(int i = 0; i < nums.size(); i++) {
        int value = target-nums[i];
        auto it = find(nums.begin()+i+1, nums.end(), value);
if(it == nums.end()) {
            continue;
} else {
            result.push_back(i);
            result.push_back(it-nums.begin());
            break;
        }
    }
        
        return result;
    }
};

3. Third Approach — Using hash table (unordered map)

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