# 167. Two Sum II - Input array is sorted

catepk·2021년 8월 25일
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## LeetCode

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68/88 167. Two Sum II - Input array is sorted

### 문제

Given an array of integers numbers that is already sorted in non-decreasing order, find two numbers such that they add up to a specific target number.

Return the indices of the two numbers (1-indexed) as an integer array answer of size 2, where 1 <= answer < answer <= numbers.length.

The tests are generated such that there is exactly one solution. You may not use the same element twice.

Example 1:

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.

Example 2:

Input: numbers = [2,3,4], target = 6
Output: [1,3]

Example 3:

Input: numbers = [-1,0], target = -1
Output: [1,2]

Constraints:

2 <= numbers.length <= 3 * 10^4
-1000 <= numbers[i] <= 1000
numbers is sorted in non-decreasing order.
-1000 <= target <= 1000
The tests are generated such that there is exactly one solution.

### 풀이

-----two pointers-----

class Solution:
def twoSum(self, numbers: List[int], target: int) -> List[int]:
left = 0
right = len(numbers) - 1
while not left == right:
if numbers[left] + numbers[right] < target:
left += 1
elif numbers[left] + numbers[right] > target:
right -= 1
else:
return left + 1, right + 1

-----binary search-----

class Solution:
def twoSum(self, numbers: List[int], target: int) -> List[int]:
for k, v in enumerate(numbers):
left = k + 1
right = len(numbers) - 1
expected = target - v

while left <= right:
mid = left + (right - left) // 2
if numbers[mid] < expected:
left = mid + 1
elif numbers[mid] > expected:
right = mid - 1
else:
return k + 1, mid + 1

-----functions1-----

class Solution:
def twoSum(self, numbers: List[int], target: int) -> List[int]:
for k, v in enumerate(numbers):
left = k + 1
right = len(numbers) - 1
expected = target - v
i = bisect.bisect_left(numbers[k + 1:], expected)
if i < len(numbers[k + 1:]) and numbers[i + k + 1] == expected:
return k + 1, i + k + 2

-----functions2-----

class Solution:
def twoSum(self, numbers: List[int], target: int) -> List[int]:
for k, v in enumerate(numbers):
left = k + 1
right = len(numbers) - 1
expected = target - v
nums = numbers[k + 1:]
i = bisect.bisect_left(nums, expected)
if i < len(nums) and numbers[i + k + 1] == expected:
return k + 1, i + k + 2

-----functions3-----

class Solution:
def twoSum(self, numbers: List[int], target: int) -> List[int]:
for k, v in enumerate(numbers):
left = k + 1
right = len(numbers) - 1
expected = target - v
i = bisect.bisect_left(numbers, expected, k + 1) # set lower bound
if i < len(numbers) and numbers[i] == expected:
return k + 1, i + 1