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Two Sum

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Question

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

You may assume that each input would have exactly one solution, and you may not use the same element twice.

Example:
Given nums = [2, 7, 11, 15], target = 9,
Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].

Solution

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/*
hashmap
*/
public int[] twoSum(int[] nums, int target) {
    Map<Integer, Integer> map = new HashMap<Integer, Integer>();
    for ( int i = 0; i< nums.length; i++){
        int n = target-nums[i];
        if ( map.containsKey(n) ){
            return new int[] {map.get(n),i};
        }else{
            map.put(nums[i],i);
        }
    }
    
    return new int[] {};
}