1. Two Sum, twosum

1. Two Sum, twosum

Question:

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

The function twoSum shocould 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 wowould have exactly one solution.

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

Question:

Use HashMap to traverse the array at a Time. Time Complexity-O (n) and Space Complexity-O (n)

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

 

Reference:

Http://www.cnblogs.com/springfor/p/3859618.html