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120. Two Sum — Indices with Target Sum

Easy

Problem Description

Given an array of $N$ integers and a target $T$ , find the two distinct 0-based indices whose values sum to $T$ . Output the indices in ascending order separated by space. If no pair exists, print -1 -1.

Input Format

•Line 1: Two space-separated integers $N$ and $T$ .
•Line 2: $N$ space-separated integers $A_0, \dots, A_{N-1}$ .

Output Format

Print the two 0-based indices separated by space, or -1 -1.

Example 1:

Input:

4 9
2 7 11 15

Output:

0 1

Explanation: A[0] + A[1] = 2 + 7 = 9.

Example 2:

Input:

3 6
3 2 4

Output:

1 2

Explanation: A[1] + A[2] = 2 + 4 = 6.

Example 3:

Input:

2 6
3 3

Output:

0 1

Explanation: A[0] + A[1] = 3 + 3 = 6.

Constraints:

Standard integer bounds: 32-bit signed integer or input range [1, 10^5].
Time complexity target: O(N) or O(N log N) where applicable.
Auxiliary space target: O(1) or minimal auxiliary memory.

Follow up:Can this algorithm be adapted to an online streaming setting where the entire input cannot be held in memory simultaneously?

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