解题思路:dp[i]表示到第i个位置有多少种解码方式。
class Solution { public: int numDecodings(string s) { int n = s.size(); int* dp = new int[n+1]; dp[0] = 1; for (int i = 1; i <= n; i++) { dp[i] = (s[i-1] == '0' ? 0 : dp[i-1]); if (i >= 2) { int k = (s[i-2] - '0') * 10 + s[i-1] - '0'; if (s[i-2] != '0' && k > 0 && k <= 26) dp[i] += dp[i-2]; } } int ans = dp[n]; delete[] dp; return ans; } };