# Python solution with detailed explanation

• Solution

Two Sum II - Input array is sorted https://leetcode.com/problems/two-sum-ii-input-array-is-sorted/?tab=Description

Binary Search

• For every element x, search its complement using binary search.
``````class Solution(object):
def b_search(self, nums, low, high, target):
while low <= high:
mid = low + ((high-low)>>1)
if nums[mid] == target:
return mid
elif nums[mid] > target:
high = mid - 1
else:
low = mid + 1
return -1

def twoSum(self, numbers, target):
"""
:type numbers: List[int]
:type target: int
:rtype: List[int]
"""
result = []
high = len(numbers)-1
for i in range(len(numbers)):
comp = target-numbers[i]
idx = self.b_search(numbers, i+1, high, comp)
if idx != -1:
result.append(i+1)
result.append(idx+1)
break
return result
``````

Two Pointers

• Keep 2 pointers start and end and keep adjusting them.
``````class Solution(object):
def twoSum(self, numbers, target):
"""
:type numbers: List[int]
:type target: int
:rtype: List[int]
"""
s,e = 0, len(numbers)-1
while s < e:
if numbers[s] + numbers[e] == target:
return [s+1, e+1]
elif numbers[s] + numbers[e] < target:
s = s+1
else:
e = e-1
return [None, None]
``````

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