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91.decode-ways.java
38 lines (33 loc) · 1.13 KB
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91.decode-ways.java
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class Solution {
public int numDecodings(String s) {
if(s.length() == 1)
return s.charAt(0) != '0' ? 1 : 0;
if(s.charAt(0) == '0')
return 0;
int prev = (s.charAt(s.length()-2)-'0' )*10 + s.charAt(s.length()-1)-'0';
int a = s.charAt(s.length()-1) != '0' ? 1 : 0;
int b = a == 1 || prev <= 26 && s.charAt(s.length()-2) != '0' ? 1 : 0;
int len = s.length()-1;
while(len >= 0 && s.charAt(len) == '0')
len--;
if(len == s.length()-1)
len--;
for(int i=len;i>=0;i--){
if(s.charAt(i) == '0' && s.charAt(i+1) == '0' || s.charAt(i)-'0' > 2 && s.charAt(i+1) == '0')
return 0;
int num = (s.charAt(i)-'0')*10 + (s.charAt(i+1)-'0') ;
if(s.charAt(i+1) != '0' && s.charAt(i) != '0' && num <= 26)
{
int tmp = b;
b = a+b;
a = tmp;
}
else{
a = b;
}
if(s.charAt(i+1) == '0')
i--;
}
return b;
}
}