[leetcode]167. Two Sum II - Input array is sorted@Java解題報告__Java

自從實習以後許久沒有做演算法題了，馬上要校招了，重新開始刷題

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

public class P167_TwoSumII_InputArrayIsSorted {    /*    解法一     */    public int[] twoSum(int[] numbers, int target) {        int l = 0, r = numbers.length - 1;        while (l < r) {            if (numbers[l] + numbers[r] == target) {                int[] res = {l + 1, r + 1};                return res;            } else if (numbers[l] + numbers[r] > target)                r--;            else                l++;        }        throw new RuntimeException("The input has no solution");    }    /*    解法二     */    public int[] twoSum1(int[] numbers, int target) {        if (numbers == null || numbers.length == 0)            return null;        int[] res = new int[2];        int index;        for (int i = 0; i < numbers.length; i++) {            index = binarySearch(numbers, target - numbers[i], i + 1, numbers.length - 1);            if (index != -1) {                res[0] = i + 1;                res[1] = index + 1;                return res;            }        }        return res;    }    private int binarySearch(int[] arr, int k, int start, int end) {        int mid;        int left = start, right = end;        while (left <= right) {            mid = left + (right - left) / 2;            if (arr[mid] > k)                right = mid - 1;            else if (arr[mid] < k)                left = mid + 1;            else                return mid;        }        return -1;    }    @Test    public void test1() {        int[] arr = {2, 3, 4};        int[] res = twoSum(arr, 6);        for (int i = 0; i < res.length; i++) {            System.out.println(res[i]);        }    }}