Decode Ways 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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    dp[1] = s.charAt(0) == '0' ? 0 : 1;
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    for (int i = 2; i <= s.length(); i++) {
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      int oneDigit = Integer.valueOf(s.substring(i - 1, i));
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      int twoDigit = Integer.valueOf(s.substring(i - 2, i));
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      if (oneDigit >= 1) {
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        dp[i] += dp[i - 1];
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      }
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      if (twoDigit >= 10 && twoDigit <= 26) {
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        dp[i] += dp[i - 2];
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      }
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    }
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    return dp[s.length()];
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  }
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}