Interleaving String Problem


Description

LeetCode Problem 97.

Given strings s1, s2, and s3, find whether s3 is formed by an interleaving of s1 and s2.

An interleaving of two strings s and t is a configuration where they are divided into non-empty substrings such that:

  • s = s1 + s2 + … + sn
  • t = t1 + t2 + … + tm
  • n - m <= 1
  • The interleaving is s1 + t1 + s2 + t2 + s3 + t3 + … or t1 + s1 + t2 + s2 + t3 + s3 + …

Note: a + b is the concatenation of strings a and b.

Example 1:

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Input: s1 = "aabcc", s2 = "dbbca", s3 = "aadbbcbcac"
Output: true

Example 2:

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Input: s1 = "aabcc", s2 = "dbbca", s3 = "aadbbbaccc"
Output: false

Example 3:

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Input: s1 = "", s2 = "", s3 = ""
Output: true

Constraints:

  • 0 <= s1.length, s2.length <= 100
  • 0 <= s3.length <= 200
  • s1, s2, and s3 consist of lowercase English letters.


Sample C++ Code

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bool isInterleave(string s1, string s2, string s3) {
    if (s3.length() != s1.length() + s2.length())
        return false;
    
    bool table[s1.length()+1][s2.length()+1];
    
    for (int i=0; i<s1.length()+1; i++)
        for (int j=0; j< s2.length()+1; j++){
            if (i==0 && j==0)
                table[i][j] = true;
            else if (i == 0)
                table[i][j] = (table[i][j-1] && s2[j-1] == s3[i+j-1]);
            else if (j == 0)
                table[i][j] = (table[i-1][j] && s1[i-1] == s3[i+j-1]);
            else
                table[i][j] = (table[i-1][j] && s1[i-1] == s3[i+j-1]) || 
                        (table[i][j-1] && s2[j-1] == s3[i+j-1]);
        }
        
    return table[s1.length()][s2.length()];
}




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