題目：

題解：

func numDecodings(s string) int {n := len(s)// a = f[i-2], b = f[i-1], c = f[i]a, b, c := 0, 1, 0for i := 1; i <= n; i++ {c = 0if s[i-1] != '0' {c += b}if i > 1 && s[i-2] != '0' && ((s[i-2]-'0')*10+(s[i-1]-'0') <= 26) {c += a}a, b = b, c}return c
}