#0032

Two Sum Indices

EasyDSA15 min10 XP

Problem

Given nums and target, return two indices whose values add to target. You may assume exactly one solution and cannot use the same element twice.

Why This Matters

Two Sum is the classic example of replacing a nested loop with a hash map of values already seen.

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 = 9.

Constraints

Exactly one valid answer exists.
Return indices, not values.
Do not use the same index twice.

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 / 4 hidden categories

Classic pair

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

Expected[0, 1]

The complement of 7 is 2, which was seen earlier.

Duplicate values

Input[3, 3], 6

Expected[0, 1]

The same value can appear twice, but the same index cannot be reused.

Hidden Test Categories

Negative numbersPair appears lateTarget is zeroLarge input