InterleavingString.java

/**
 * Given s1, s2, s3, find whether s3 is formed by the interleaving of s1 and s2.
 *
 * <p>For example, Given: s1 = "aabcc", s2 = "dbbca",
 *
 * <p>When s3 = "aadbbcbcac", return true. When s3 = "aadbbbaccc", return false.
 */
public class InterleavingString {
  public boolean isInterleave(String s1, String s2, String s3) {
    if (s1.length() + s2.length() != s3.length()) return false;
    boolean[][] mat = new boolean[s1.length() + 1][s2.length() + 1];
    mat[0][0] = true;
    for (int i = 1; i <= s1.length(); ++i)
      mat[i][0] = mat[i - 1][0] && (s3.charAt(i - 1) == s1.charAt(i - 1));
    for (int i = 1; i <= s2.length(); ++i)
      mat[0][i] = mat[0][i - 1] && (s3.charAt(i - 1) == s2.charAt(i - 1));
    for (int i = 1; i <= s1.length(); ++i)
      for (int j = 1; j <= s2.length(); ++j)
        mat[i][j] =
            (mat[i][j - 1] && s2.charAt(j - 1) == s3.charAt(i + j - 1))
                || (mat[i - 1][j] && s1.charAt(i - 1) == s3.charAt(i + j - 1));
    return mat[s1.length()][s2.length()];
  }
}