167. Two Sum II - Input array is sorted
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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. 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.
Input: numbers={2, 7, 11, 15}, target=9
Output: index1=1, index2=2
这个和two sum的区别就是这个数组是有序的,并且最后输出的index需要+1
解决two sum的时候由于数组无序,直接使用了暴力搜索的方式,虽然可以AC但是效率很低,其实只要对数组进行一次排序,就和这个是一个问题了。
解决方案:
由于数组是有序的,可以对数组两端的加和进行判断,如果大于target,那尾端就向前移动,反之就让头指针向后,知道加和和target想等为止。
代码如下:
class Solution {
func twoSum(_ numbers: [Int], _ target: Int) -> [Int] {
var array = [Int]()
var start: Int = 0
var end: Int = numbers.count - 1
while (start < end) {
if target == numbers[start] + numbers[end] {
array = [start + 1, end + 1]
break
}
else if target < numbers[start] + numbers[end] {
end -= 1
}
else {
start += 1
}
}
return array
}
}
运行时间:
38ms
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