#0231

Two Sum Indexes

EasyDSA18 min10 XP

Problem

Given a list of integers and a target, return the two indexes whose values add to target. Return the smaller index first.

Why This Matters

Two Sum is the classic shift from nested-loop thinking to remembering useful past values.

Function Signature

def two_sum(nums, target):

Examples

Example 1

Inputnums = [2, 7, 11, 15], target = 9

Output[0, 1]

nums[0] + nums[1] is 2 + 7, which equals 9.

Constraints

Return the exact requested value.
Handle empty or small inputs when the prompt allows them.
Prefer the target DSA pattern over brute force when the input can grow.

CodePython

def two_sum(nums, target):
    """
    Input example: nums = [2, 7, 11, 15], target = 9
    Return: [0, 1]
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    # write your code here
    return []

def two_sum(nums, target):
    """
    Input example: nums = [2, 7, 11, 15], target = 9
    Return: [0, 1]
    Return the value from the function so the tests can compare it. Do not print unless the prompt asks.
    """
    # write your code here
    return []

Visible browser tests run here when available.

Testcases2 visible / 3 hidden categories

Front pair

Input[2, 7, 11, 15], target = 9

Expected[0, 1]

The first two values make the target.

Repeated values

Input[3, 3, 4], target = 6

Expected[0, 1]

The same value can be used from two different indexes.

Hidden Test Categories

negative numberspair appears lateno pair returns empty list