Count Pairs with Sum K
EasyP2Coding
Return the number of pairs of indices (i, j) with i < j such that nums[i] + nums[j] == k.
Equal values at different indices form different pairs.
Example 1
- Input
- nums = [1,2,3,4], k = 5
- Output
- 2
- Why
- (1,4) and (2,3).
Example 2
- Input
- nums = [1,1,1], k = 2
- Output
- 3
- Why
- Three indices give three pairs of 1 + 1.
Example 3
- Input
- nums = [], k = 5
- Output
- 0
Constraints
- 0 <= nums.length <= 10^5
- -10^9 <= nums[i], k <= 10^9
Hints
Give it a real attempt first. Run shows which examples fail.
Saved automatically
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