Leetcode-1:Two Sum

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].

思路：用哈希表将targets - num[i]的值作为健，索引作为值存下来，当访问到num[j]时，如果哈希表内存在num[j]，那么返回j和hash[num[j]]。

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