leetcode-1-Two Sum

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description

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].

common method

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class Solution {
    public int[] twoSum(int[] nums, int target) {
        int[] ret = new int[2];
        for(int i =0; i<nums.length-1 ;i++){
            for (int j = i+1 ;j < nums.length ;j++ ){
                if (nums[i] + nums[j] == target){
                    ret = new int[]{i, j};
                    return ret;
                }
            }
        }
        return ret ;
    }
}

best method

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