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

1. Two Sum.java

public class Solution {
    public int[] twoSum(int[] nums, int target) {
        
        HashMap<Integer,Integer> bufferMap = new HashMap<Integer,Integer>();
        int[] res = new int[2];
        
        for(int i = 0; i< nums.length; i++){
            if(bufferMap.containsKey(nums[i])){
                res[0] = bufferMap.get(nums[i]);
                res[1] = i;
                return res;
            }
            
            bufferMap.put(target - nums[i],i);
            
        }
        return res;
    }
}

1. Two Sum.py

class Solution(object):
    def twoSum(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: List[int]
        """
        
        
        buffer_dict = {}; #Use a dictionary to store the valur target - nums[i],the time complexity is O(n)
        
        for i in range(len(nums)):
            if nums[i] in buffer_dict:
                return [buffer_dict[nums[i]], i];
            else:
                buffer_dict[target - nums[i]] = i;