05 August 2008
跟91比多了个星号*，可以作为任意单个数字
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
class Solution {
/*
https://leetcode.com/problems/decode-ways-ii/discuss/105275/Java-DP-O(n)-time-and-O(1)-space
DP, O(n) time and O(1) space
*/
public int numDecodings(String s) {
long[] res = new long[2];
res[0] = ways(s.charAt(0));
if (s.length() < 2) {
return (int)res[0];
}
res[1] = res[0] * ways(s.charAt(1)) + ways(s.charAt(0), s.charAt(1));
for (int j = 2; j < s.length(); j++) {
long temp = res[1];
res[1] = (res[1] * ways(s.charAt(j)) + res[0] * ways(s.charAt(j-1), s.charAt(j))) % 1000000007;
res[0] = temp;
}
return (int)res[1];
}
private static int ways(int ch) {
if (ch == '*') {
return 9;
}
if (ch == '0') {
return 0;
}
return 1;
}
private static int ways(char ch1, char ch2) {
String str = "" + ch1 + "" + ch2;
if (ch1 != '*' && ch2 != '*') {
if (Integer.parseInt(str) >= 10 && Integer.parseInt(str) <= 26) {
return 1;
}
} else if (ch1 == '*' && ch2 == '*') {
return 15;
} else if (ch1 == '*') {
if (Integer.parseInt("" + ch2) >= 0 && Integer.parseInt("" + ch2) <= 6) {
return 2;
} else {
return 1;
}
} else {
if (Integer.parseInt("" + ch1) == 1) {
return 9;
} else if (Integer.parseInt("" + ch1) == 2) {
return 6;
}
}
return 0;
}
}