Longest Common Substring

Given 2 string str1 and str2 we have to find the length of the longest common substring between them.

Examples

Input : X = “abcdxyz”, y = “xyzabcd” Output : 4

The longest common substring is “abcd” and is of length 4.

Input : X = “zxabcdezy”, y = “yzabcdezx” Output : 6

The longest common substring is “abcdez” and is of length 6.

Implementation in Java

public int getLongestCommonSubstring(String str1,String str2){
        int arr[][] = new int[str2.length()+1][str1.length()+1];
        int max = Integer.MIN_VALUE;
        for(int i=1;i<=str2.length();i++){
            for(int j=1;j<=str1.length();j++){
                if(str1.charAt(j-1) == str2.charAt(i-1)){
                    arr[i][j] = arr[i-1][j-1]+1;
                    if(arr[i][j]>max)
                        max = arr[i][j];
                }
                else
                    arr[i][j] = 0;
            }
        }
        return max;
    }

Time Complexity

O(m*n)

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