two-sum-iv-check-before-insert

Status: IN

`findTarget` prevents self-pairing by checking the `seen` set *before* inserting the current node's value — the ordering of check-then-add is the critical invariant.

Source: entries/2026/06/06/two-sum-iv-input-is-a-bst-solution.md

Depended on by

• two-sum-family-spans-lookup-strategy-space

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