# OstiumLinkUpKeep:removeFromWatchList() complexity could be reduced Low/Info · Three Sigma · RWA perpetuals DEX · 19th February, 2024 Finding 3S-OS-N24 of the Ostium security review. - Protocol: https://www.ostium.com/ - Report: /reports/ostium - Source: https://cdn.sanity.io/files/qoqld077/production/a95b9c69e0f65d1d6b0e649f0d62a362358ca8ce.pdf --- ### Description [OstiumLinkUpKeep:removeFromWatchList()](https://github.com/0xOstium/smart-contracts-threeSigma/blob/dev/src/OstiumLinkUpKeep.sol#L163) currently iterates over the full s_registryWatchLists to find the keeperIds and delete them if equal. This has O(n^2) complexity, which could cost a significant amount of gas. ### Recommendation One way to tackle this problem is tweaking the isInWatchList mapping to store the index of the array instead of a bool, adding 1 to each index so that 0 is not a valid index and can be used to check for abcense. This way, when removing, the index can be fetchd from the corresponding mapping. ### Status Acknowledged