Two sum less than k

Array Two Pointers Binary Search Sorting

62.1% acceptance

Mar 31, 2026

1173

135

Given an array nums of integers and integer k, return the maximum sum such that there exists i < j with nums[i] + nums[j] = sum and sum < k. If no i, j exist satisfying this equation, return -1.

Solution

Rust

Time O(n log n)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn two_sum_less_than_k(mut nums: Vec<i32>, k: i32) -> i32 {
    nums.sort_unstable();
    let mut ans = -1;
    let (mut lo, mut hi) = (0, nums.len() - 1);
    while lo < hi {
      let sum = nums[lo] + nums[hi];
      if sum < k {
        ans = ans.max(sum);
        lo += 1;
      } else {
        hi -= 1;
      }
    }
    ans
  }
}