类似于爬楼梯
string s; using namespace std; class Solution { public: int numDecodings(string s) { if( s.empty() || s.size() >= 1 && s[0] == '0' ) { return 0; } int n = s.size(); int dp[n+2]; dp[0] = 1; for( int i = 0; i < s.size(); i++ ) { if( s[i] != '0' ) dp[i+1] = dp[i]; else dp[i+1] = 0; if( i >= 1 && ( ( s[i-1] == '1' ) || ( s[i-1] == '2' ) && ( s[i] <= '6' ) ) ) dp[i+1] += dp[i-1]; } return dp[n]; } };