leetcode001——Two Sum

一、题目描述

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

二、解题思路及代码

可以采用哈希表的方法，key记为numbers中的数字，value记为相应数字的位置，每次查看target-当前数字是否出现过即可。

代码如下（224ms）

import java.util.Hashtable;
public class Solution {
public int[] twoSum(int[] numbers, int target) {
int[] result = new int[2];
result[0] = 0;
result[1] = 0;
Hashtable table = new Hashtable();

for(int i = 0; i < numbers.length; i++) {
if(table.containsKey(target - numbers[i])) {
result[0] = (int)table.get(target-numbers[i]) + 1;
table.put(numbers[i],i);
result[1] = (int)table.get(numbers[i]) + 1;
}
else {
table.put(numbers[i],i);
}
}
return result;
}
}