int numDecodings(string s) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
if( s.length() < 1)
return 0;
if(caches.find(s) != caches.end())
{
return caches[s];
}
if(s[0] == '0')
return caches[s]= 0;
if(s.length() > 1)
{
if( s[0] == '1' || ( s[0] == '2' && s[1] < '7'))
{
int sum1 = numDecodings(s.substr(1));
int sum2 = 1;
if( s.length() > 2)
{
sum2 = numDecodings(s.substr(2));
}
return sum1 + sum2;
}
else
{
return caches[s] = numDecodings(s.substr(1));
}
}
return caches[s] = 1;
}
int main() {
char s[] = "201";
int ans = numDecodings(s);
printf("%d\n", ans);
system("pause");
return 0;
}
int main(void){
char s[20];
while(gets(s)){
int result=numDecodings(s);
printf("%d\n",result);
}
}
int numDecodings(string& s, int i)
{
if(i == s.length())
return 1;
if(memory[i] != -1)
return memory[i];
if(s[i] == '0')
return 0;
if((s[i] == '1' && i+1 < s.length() && s[i+1] != '0') || (s[i] == '2' && i+1 < s.length() && s[i+1] >= '1' && s[i+1] <= '6'))
{
if(i+2 < s.length() && s[i+2] == '0')
{
int res = numDecodings(s, i+1);
memory[i] = res;
return res;
}
int res1, res2;
res1 = numDecodings(s, i+1);
if(res1)
res2 = numDecodings(s, i+2);
else
res2 = 0;
memory[i] = res1+res2;
return memory[i];
}
if((s[i] == '1' && i+1 < s.length() && s[i+1] == '0') || (s[i] == '2' && i+1 < s.length() && s[i+1] == '0'))
{
int res = numDecodings(s, i+2);
memory[i] = res;
return res;
}
int res = numDecodings(s, i+1);
memory[i] = res;
return res;
}
int numDecodings(string s) {
if(s.length() == 0)
return 0;
memory = new int[s.length()];
for(int i = 0; i < s.length(); i++)
memory[i] = -1;
return numDecodings(s, 0);
}
int numDecodings(char* s) {
if(s==NULL) return 0;
int len=strlen(s);
if(len==0) return 0;
for(int i=0;i<len;i++){//先检查是否有非法字符
if(!(s[i]>='0'&&s[i]<='9')){
return 0;
}
}
if(len==1){
if(s[0]=='0') return 0;
else return 1;
}
int result=0;
//下面为大于等于2的情况。
if(s[0]=='1'||(s[0]=='2'&&s[1]<='6')){
result= numDecodings(s+1)+numDecodings(s+2);
}
else{
result= numDecodings(s+1);
}
return result+1;
}
