Python: Find a pair of elements from a given array whose sum equals a specific target number
Python Class: Exercise-5 with Solution
Write a Python class to find a pair of elements (indices of the two numbers) from a given array whose sum equals a specific target number.
Difficulty: Medium. Company: Google, Facebook
Sample Solution-1:
Python Code:
class py_solution:
def twoSum(self, nums, target):
lookup = {}
for i, num in enumerate(nums):
if target - num in lookup:
return (lookup[target - num], i )
lookup[num] = i
print("index1=%d, index2=%d" % py_solution().twoSum((10,20,10,40,50,60,70),50))
Sample Output:
index1=2, index2=3
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Sample Solution-2:
Python Code:
class py_solution(object):
def twoSum(self, nums, target_num):
"""
:type nums: list[int]
:type target: int
:return type: list[int]
"""
result_dict = dict()
pos = 0
while pos < len(nums):
if (target_num - nums[pos]) not in result_dict:
result_dict[nums[pos]] = pos
pos += 1
else:
return [result_dict[target_num - nums[pos]], pos]
print(py_solution().twoSum([10,20,10,40,50,60,70],50))
print(py_solution().twoSum([10,20,10,40,50,60,70],52))
Sample Output:
[2, 3] None
Flowchart:
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Python Code Editor:
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Previous: Write a Python class to get all possible unique subsets from a set of distinct integers.
Next: Write a Python class to find the three elements that sum to zero from a set (array) of n real numbers.
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Python: Tips of the Day
Find current directory and file's directory:
To get the full path to the directory a Python file is contained in, write this in that file:
import os dir_path = os.path.dirname(os.path.realpath(__file__))
(Note that the incantation above won't work if you've already used os.chdir() to change your current working directory, since the value of the __file__ constant is relative to the current working directory and is not changed by an os.chdir() call.)
To get the current working directory use
import os cwd = os.getcwd()
Documentation references for the modules, constants and functions used above:
- The os and os.path modules.
- The __file__ constant
- os.path.realpath(path) (returns "the canonical path of the specified filename, eliminating any symbolic links encountered in the path")
- os.path.dirname(path) (returns "the directory name of pathname path")
- os.getcwd() (returns "a string representing the current working directory")
- os.chdir(path) ("change the current working directory to path")
Ref: https://bit.ly/3fy0R6m
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