[leetcode]167. Two Sum II - Input array is sorted@Java解题报告

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/zjkC050818/article/details/79432834

自从实习以后许久没有做算法题了，马上要校招了，重新开始刷题

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]);
        }
    }


}