Longest Common Substring

Source

• lintcode: Longest Common Substring

Given two strings, find the longest common substring.

Return the length of it.

Example
Given A = "ABCD", B = "CBCE", return 2.

Note
The characters in substring should occur continuously
in original string. This is different with subsequence.

Challenge
O(n x m) time and memory.

Java

public class Solution {
    /**
     * @param A, B: Two string.
     * @return: the length of the longest common substring.
     */

    public int longestCommonSubstring(String A, String B) {
        if (A == null || A.length() == 0 || B == null || B.length() == 0) {
            return 0;
        }

        int[][] dp = new int[A.length() + 1][B.length() + 1];
        int lcs = 0;

        for (int i = 1; i <= A.length(); i++) {
            for (int j = 1; j <= B.length(); j++) {
                if (A.charAt(i - 1) == B.charAt(j - 1)) {
                    dp[i][j] = dp[i - 1][j - 1] + 1;
                }
                lcs = Math.max(lcs, dp[i][j]);
            }
        }
        return lcs;
    }
}

Reference

Longest Common Substring