1.java

//1. Two Sum
// Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target.
// You may assume that each input would have exactly one solution, and you may not use the same element twice.
// You can return the answer in any order.

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