Two Sum

Given an array of integers, find two numbers such that they add up to a specific target number.

The function twoSum should return indices of the two numbers such that they add up to the target, where index1 must be less than index2. Please note that your returned answers (both index1 and index2) are not zero-based.

You may assume that each input would have exactly one solution.

Input: numbers={2, 7, 11, 15}, target=9
Output: index1=1, index2=2

 

最早我使用的方法是兩個for循環的方法，時間複雜度爲O(n2)。可是，在線測試提示時間超時，所以必須考慮更加簡單的方法，

public class Solution {
    public int[] twoSum(int[] numbers, int target) {
        int[]temp = new int[2];
        Map<Integer,Integer>map = new HashMap<Integer,Integer>();
        for(int i = 0;i<numbers.length;i++){
            if(map.get(numbers[i])==null){
                map.put(numbers[i],i);
            }
            if(map.containsKey(target-numbers[i])&& i !=map.get(target-numbers[i])){
                temp[1] = i+1;
                temp[0] = map.get(target-numbers[i])+1;
                return temp;
            }
        }
        return temp;
    }
}