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_639.java
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38 lines (36 loc) · 1.55 KB
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package com.fishercoder.solutions;
public class _639 {
public static class Solution1 {
/**
* reference: https://leetcode.com/articles/decode-ways-ii/#approach-2-dynamic-programming-accepted
*/
int m = 1000000007;
public int numDecodings(String s) {
long[] dp = new long[s.length() + 1];
dp[0] = 1;
dp[1] = s.charAt(0) == '*' ? 9 : s.charAt(0) == '0' ? 0 : 1;
for (int i = 1; i < s.length(); i++) {
if (s.charAt(i) == '*') {
dp[i + 1] = 9 * dp[i];
if (s.charAt(i - 1) == '1') {
dp[i + 1] = (dp[i + 1] + 9 * dp[i - 1]) % m;
} else if (s.charAt(i - 1) == '2') {
dp[i + 1] = (dp[i + 1] + 6 * dp[i - 1]) % m;
} else if (s.charAt(i - 1) == '*') {
dp[i + 1] = (dp[i + 1] + 15 * dp[i - 1]) % m;
}
} else {
dp[i + 1] = s.charAt(i) != '0' ? dp[i] : 0;
if (s.charAt(i - 1) == '1') {
dp[i + 1] = (dp[i + 1] + dp[i - 1]) % m;
} else if (s.charAt(i - 1) == '2' && s.charAt(i) <= '6') {
dp[i + 1] = (dp[i + 1] + dp[i - 1]) % m;
} else if (s.charAt(i - 1) == '*') {
dp[i + 1] = (dp[i + 1] + (s.charAt(i) <= '6' ? 2 : 1) * dp[i - 1]) % m;
}
}
}
return (int) dp[s.length()];
}
}
}