Decode Ways II LeetCode solution in Java

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class Solution {
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  public int numDecodings(String s) {
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    int[] dp = new int[s.length() + 1];
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    dp[0] = 1;
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    int M = (int) 1e9 + 7;
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    for (int i = 1; i <= s.length(); i++) {
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      for (int j = 1; j <= 26; j++) {
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        if (j < 10
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            && (s.charAt(i - 1) - '0' == j
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                || s.charAt(i - 1) == '*')) { // 1 digit -> if they are equal or if *
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          dp[i] += dp[i - 1];
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          dp[i] %= M;
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        }
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        if (i > 1 && j >= 10 && ok(j, s.substring(i - 2, i))) { // ok() function handles 2 digits
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          dp[i] += dp[i - 2];
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          dp[i] %= M;
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        }
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      }
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    }
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    return dp[s.length()];
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  }
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  private boolean ok(int val, String s) { // TRUE if the value s represents can equal to val.
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    return (s.equals("**") && val % 10 > 0
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        || s.charAt(0) == '*' && val % 10 == s.charAt(1) - '0'
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        || s.charAt(1) == '*' && val / 10 == s.charAt(0) - '0' && val % 10 > 0
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        || !s.contains("*") && Integer.parseInt(s) == val);
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  }
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}