Title
A message containing letters from A-Z is being encoded to numbers using the following mapping: ‘A’ -> 1 ‘B’ -> 2 … ‘Z’ -> 26 Given a non-empty string containing only digits, determine the total number of ways to decode it.
Example 1:
Input: “12”
Output: 2
Explanation: It could be decoded as “AB” (1 2) or “L” (12).
Example 2:
Input: “226”
Output: 3
Explanation: It could be decoded as “BZ” (2 26), “VF” (22 6), or “BBF” (2 2 6).
Solution
动态规划
容易错误的测试用例有1,01,101
//cpp:
class Solution {
public:
int numDecodings(string s) {
if (s.length() == 0) return 0;
vector<int> dp(s.length()+2);
dp[s.length() - 1] = s[s.length() - 1] == '0' ? 0 : 1;
dp[s.length()] = 1;
for (int i = s.length() - 2; i >= 0; i--) {
dp[i] = dp[i + 1];
if (s[i] == '0') {
dp[i] = 0;
continue;
}
if (stoi(s.substr(i, 2)) <= 26) {
dp[i] += dp[i + 2];
}
cout << dp[i] << endl;
}
return dp[0];
}
};