Approach #1 (Brute Force)

LeetCode_1. Two Sum.cpp

/* 
test input:
[2,7,11,15]
9
------------
output:
[0, 1]
------------
*/
class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        int i,j;
        for(i=0; i<nums.size(); i++){
            for(j=0; j<nums.size(); j++){
                if(nums[i]+nums[j]==target && i!=j){
                    vector<int> ans;
                    ans.push_back(i);
                    ans.push_back(j);
                    return ans;
                }
            }
        }
    }
};

void trimLeftTrailingSpaces(string &input) {
    input.erase(input.begin(), find_if(input.begin(), input.end(), [](int ch) {
        return !isspace(ch);
    }));
}

void trimRightTrailingSpaces(string &input) {
    input.erase(find_if(input.rbegin(), input.rend(), [](int ch) {
        return !isspace(ch);
    }).base(), input.end());
}

vector<int> stringToIntegerVector(string input) {
    vector<int> output;
    /*trimLeftTrailingSpaces(input);
    trimRightTrailingSpaces(input);
    input = input.substr(1, input.length() - 2);
    stringstream ss;
    ss.str(input);
    string item;
    char delim = ',';
    while (getline(ss, item, delim)) {
        output.push_back(stoi(item));
    }*/
    istringstream ss(input);
    int item;
    char c;
    while(ss >> c >> item){
        output.push_back(item);
    }
    return output;
}

int stringToInteger(string input) {
    return stoi(input);
}

string integerVectorToString(vector<int> list, int length = -1) {
    if (length == -1) {
        length = list.size();
    }

    if (length == 0) {
        return "[]";
    }

    string result;
    for(int index = 0; index < length; index++) {
        int number = list[index];
        result += to_string(number) + ", ";
    }
    return "[" + result.substr(0, result.length() - 2) + "]";
}

int main() {
    string line;
    while (getline(cin, line)) {
        vector<int> nums = stringToIntegerVector(line);
        getline(cin, line);
        int target = stringToInteger(line);
        
        vector<int> ret = Solution().twoSum(nums, target);

        string out = integerVectorToString(ret);
        cout << out << endl;
    }
    return 0;
}

hash table
class Solution { public: vector<int> twoSum(vector<int>& nums, int target) { map<int, int> hashTable; vector<int> outVec; int i; for(i=0; i<nums.size(); i++){ map<int, int>::iterator it = hashTable.find(target-nums[i]); if(it != hashTable.end()){ outVec.push_back(it->second); outVec.push_back(i); return outVec; } hashTable.insert(pair<int, int>(nums[i],i)); } } };