0167._Two_Sum_II_-_Input_array_is_sorted

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167. Two Sum II - Input array is sorted

难度: Easy

刷题内容

原题连接

内容描述

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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.

Note:

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.
Example:

Input: numbers = [2,7,11,15], target = 9
Output: [1,2]
Explanation: The sum of 2 and 7 is 9. Therefore index1 = 1, index2 = 2.

解题方案

思路 1
**- 时间复杂度: O(log2 N)**- 空间复杂度: O(n)**

  • 使用贪心算法，用左右的数字开始加，如果数字大于目标right–，反之left++

代码：

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/**
 * @param {number[]} numbers
 * @param {number} target
 * @return {number[]}
 */
var twoSum = function(numbers, target) {
    if(numbers.length===0)
        return [];
    var left = 0,right = numbers.length-1;
    while(right>left){
        if(numbers[right]+numbers[left]>target)
            right--;
        else if(numbers[right]+numbers[left]<target)
            left++;
        else return [left+1,right+1];
    }
    return [];
};