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639.java
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639.java
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__________________________________________________________________________________________________
sample 7 ms submission
class Solution {
public int numDecodings(String ss) {
char[] s = ss.toCharArray();
int last = s.length-1;
long z0 = 1, z1 = 1, z2;
char d = 127, dd;
for (int i = last; i >= 0; i--) {
dd = d;
d = s[i];
z2 = z1; z1 = z0; z0 = 0;
if (d == '*') {
z0 += z1*9;
if (dd == '*') z0 += z2*15;
else {
if (dd <= '6' && dd >= '0') z0 += 2*z2;
else if (dd <= '9' && dd >= '0') z0 += z2;
}
} else {
if (d != '0') z0 += z1;
if (dd == '*') {
if (d == '1') z0 += z2*9;
else if (d == '2') z0 += z2*6;
} else if ((d == '1' && dd >= '0' && dd <= '9') || (d == '2' && dd >= '0' && dd <= '6')) z0 += z2;
}
if ((z0 & 0x0FFF0000000000000L) > 0) z0 %= 1000000007;
}
return (int) (z0 % 1000000007);
}
}
__________________________________________________________________________________________________
sample 38924 kb submission
class Solution {
private static final int MOD = 1000000007;
public int numDecodings(String s) {
int n = s.length();
long[] dp = new long[n + 1];
dp[0] = 1;
switch (s.charAt(0)) {
case '0':
dp[1] = 0;
break;
case '*':
dp[1] = 9;
break;
default:
dp[1] = 1;
break;
}
for (int i = 2; i <= n; i++) {
if (s.charAt(i - 1) == '*') {
dp[i] = (dp[i] + 9 * dp[i - 1]) % MOD;
if (s.charAt(i - 2) == '1') {
dp[i] = (dp[i] + dp[i - 2] * 9) % MOD;
} else if (s.charAt(i - 2) == '2') {
dp[i] = (dp[i] + dp[i - 2] * 6) % MOD;
} else if (s.charAt(i - 2) == '*') {
dp[i] = (dp[i] + dp[i - 2] * 15) % MOD;
}
} else {
dp[i] = (dp[i] + s.charAt(i - 1) == '0' ? 0 : dp[i - 1]) % MOD;
if (s.charAt(i - 2) == '1') {
dp[i] = (dp[i] + dp[i - 2]) % MOD;
} else if (s.charAt(i - 2) == '2' && s.charAt(i - 1) <= '6') {
dp[i] = (dp[i] + dp[i - 2]) % MOD;
} else if (s.charAt(i - 2) == '*') {
dp[i] = (dp[i] + dp[i - 2] * (s.charAt(i - 1) > '6' ? 1 : 2)) % MOD;
}
}
}
return (int)dp[n];
}
}
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