Common Substring

Problem

Given two strings s1 and s2, find the length of the longest common substring. A substring is a contiguous sequence of characters within a string.

Examples

longestCommonFragment('MagicMirrors', 'MirroredMystics')
// returns 6
// "Mirror" is the longest echoed fragment

longestCommonFragment('EtherealEcho', 'EchoChamber')
// returns 4
// "Echo" is the echoed fragment

longestCommonFragment('SecretSanctuary', 'SanctumSanctorum')
// returns 6
// "Sanctu" is the echoed fragment