DATA STRUCTURES • ALGORITHMS

Two Sum

Finding two numbers in an array that add up to a specific target sum. In a sorted array, this can be solved efficiently using two pointers.

Time

O(N log N) (for sorting)

Space

O(1)

Key Principle 1

Two-pointer technique

Key Principle 2

Requires sorted input

Key Principle 3

Sum > Target: move right pointer

Key Principle 4

Sum < Target: move left pointer

TWO_SUM_LAB
ARRAY:
TARGET:
Current Step
Searching for sum 26 in sorted array.
Playback
Pointer Tracker ⠿
L0
R5
TARGET26
STATUSStarting
Two Pointer Logic ⠿
1int l = 0, r = n - 1;
2while (l < r) {
3    int sum = arr[l] + arr[r];
4    if (sum == target) return {l, r};
5    if (sum < target) l++;
6    else r--;
7}
2
L
7
[1]
11
[2]
15
[3]
18
[4]
22
R

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