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(N)**- 空间复杂度: O(N)**

算法来源于知乎文章——趣味算法思想

  • 由于数组是有序的，所以可以从两边向中间逐渐收敛地进行查找，好处在于避免了双重循环
  • 如果最两端的和小于目标数，则可以让左侧下标+1，然后重新进行运算比较
  • 如果最两端的和大于目标数，则可以让右侧下标-1，然后重新进行运算比较

代码：

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