Add to List 167. Two Sum II

Given an array of integers that is already sorted in ascending order, 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 and you may not use the same element twice.

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

class Solution {    public int[] twoSum(int[] numbers, int target) {        // step1: 将所有的数 存入到hashmap(字典)中去        //<K, V> ---> K one element of numbers, V is K's position in the array.        HashMap<String, Integer> dic = new HashMap<String, Integer>();        for(int i = 0; i < numbers.length; ++i) {            dic.put(numbers[i] + "", i + 1);        }                int [] res = new int[2];        // 开始搜索        int another;        for (int i = 0; i < numbers.length; ++i) {            another = (target - numbers[i]);            // 存在两个数相同            if (another == numbers[i]) {                if (i < numbers.length && another == numbers[i + 1]) {                    res[0] = i + 1;                    res[1] = i + 2;                    return res;                }                ++i;            }            if (dic.get(another + "") != null) {                res[0] = i + 1;                res[1] = dic.get(another+"");                return res;            }                                }        return null;    }}

学习笔记:

1. 这题并不难

有一点需要记住：有时数据探索使用二分法比hash快。