题目：

题解：

class Solution {public int numDecodings(String s) {int n = s.length();// a = f[i-2], b = f[i-1], c=f[i]int a = 0, b = 1, c = 0;for (int i = 1; i <= n; ++i) {c = 0;if (s.charAt(i - 1) != '0') {c += b;}if (i > 1 && s.charAt(i - 2) != '0' && ((s.charAt(i - 2) - '0') * 10 + (s.charAt(i - 1) - '0') <= 26)) {c += a;}a = b;b = c;}return c;}
}