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Letter Combinations of a Phone Number.cpp
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Letter Combinations of a Phone Number.cpp
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#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
using namespace std;
/*穷举法。注意数字[7]和数字[9]分别代表4个字符。*/
class Solution {
public:
vector<string> letterCombinations(string digits) {
int len=digits.length();
vector<string> ret;
int t=1;
for(int i=0;i<len;i++){
if(digits[i]=='7'||digits[i]=='9')
t=t*4;
else
t=t*3;
}
for(int i=0;i<t;i++){
string str;
for(int j=0;j<len;j++){
int num=digits[j]-'0';//2-9
int w;
char ch;
int p=getPow(j,digits);
if(num<7){
w=i%(3*p)/p;//0 1 2
ch=(num-2)*2+num-2+'a'+w;
}else if(num==7){
w=i%(4*p)/p;//0 1 2 3
ch=(num-2)*2+num-2+'a'+w;
}else if(num==8){
w=i%(3*p)/p;
ch=(num-2)*2+num-1+'a'+w;
}else if(num==9){
w=i%(4*p)/p;
ch=(num-2)*2+num-1+'a'+w;
}
str.push_back(ch);
}
ret.push_back(str);
}
return ret;
}
private:
int getPow(int n,string digits){
int ret=1;
for(int i=0;i<n;i++){
if(digits[i]=='7'||digits[i]=='9')
ret=ret*4;
else
ret=ret*3;
}
return ret;
}
};
int main(){
Solution solution;
string strin;
vector<string> str;
cin>>strin;
str=solution.letterCombinations(strin);
for(int i=0;i<str.size();i++)
cout<<str[i]<<endl;
system("PAUSE");
return 0;
}