3Sum Closest

medium

Find three integers whose sum is closest to target

3Sum Closest

Key Insight

Like 3Sum but track |sum - target|. Update closest when difference decreases.

Step 1Sort Array
Target: 1
-4
0
-1
1
1
2
2
3

[-1, 2, 1, -4] → [-4, -1, 1, 2]. Target = 1.

1 / 5

Learn the Pattern

Two PointersUse two pointers to traverse an array or string, reducing time complexity from O(n^2) to O(n) for problems involving pairs or subarrays.
Practice the Code

Step-by-Step Walkthrough: 3Sum Closest

Like 3Sum but track |sum - target|. Update closest when difference decreases.

  1. Sort Array

    [-1, 2, 1, -4] → [-4, -1, 1, 2]. Target = 1.

  2. Fix i=0

    -4 + (-1) + 2 = -3. Diff from target = |−3−1| = 4.

  3. Fix i=1

    -1 + 1 + 2 = 2. Diff = |2−1| = 1. Closer!

  4. Best Found

    Sum 2 is closest to target 1 (diff=1).

  5. Result

    Closest sum to 1 is 2.