https://leetcode.com/problems/two-sum-ii-input-array-is-sorted/
题解
- 二分查找O(nlogn)：有序自然想到二分查找，从左往右迭代数组每个元素
num，在后面剩下的数组元素中二分查找到target-num
var twoSum = function(numbers, target) {const binarySearch = (numbers,key,i)=>{let [start,end] = [i,numbers.length-1]while(start <= end){let mid = (start + end) >>> 1if(numbers[mid] < key){start = mid + 1;}else if(numbers[mid]> key){end = mid - 1;}else{return mid + 1 // 返回第几个，而不是索引}}return -1;}for(let i = 1 ; i <= numbers.length ; i++){ // i 从1 开始let another = binarySearch(numbers,target - numbers[i-1],i);if(another != -1){ // 找到另一个数字，返回return [i,another]}}return [0,0]
};
- 双指针O(n)， 当双指针所指数字之和小于目标值，左指针右移动；反之右指针左移
var twoSum = function(numbers, target) {let [left,right] =[0, numbers.length - 1];while (left < right) {if (numbers[left] + numbers[right] > target) {// 两数之和偏大，右指针左移right--;} else if (numbers[left] + numbers[right] < target) {// 两数之和偏小，左指针右移left++;} else { //找到两数，返回return [left + 1, right + 1];} }
};
)
