Longest Common Subsequence (LCS)?

Short answer: int LCS(string s1, string s2) { int m = s1.Length, n = s2.Length; int[,] dp = new int[m + 1, n + 1]; for (int i = 1; i <= m; i++) { for (int j = 1; j <= n; j++) { if (s1[i - 1] == s2[j - 1]) dp[i, j] = dp[i - 1, j - 1] + 1; else dp[i, j] = Math.Max(dp[i - 1, j], dp[i, j - 1]); } } return dp[m, n]; } Explanation: Build DP table comparing chars; find longest subsequence common to both strings. Follow on:

Example code

int LCS(string s1, string s2)
{
int m = s1.Length, n = s2.Length;
int[,] dp = new int[m + 1, n + 1];
for (int i = 1; i <= m; i++)
{
for (int j = 1; j <= n; j++)
{
if (s1[i - 1] == s2[j - 1])
dp[i, j] = dp[i - 1, j - 1] + 1; else dp[i, j] = Math.Max(dp[i - 1, j], dp[i, j - 1]);
}
}
return dp[m, n];
} Explanation: Build DP table comparing chars; find longest subsequence common to both strings. Follow on:

Real-world example (ShopNest)

In coding rounds, state complexity aloud, write a clear ShopNest-flavored example (orders, carts), then handle edge cases (empty list, null, overflow).

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.