链接：https://leetcode-cn.com/problems/decode-ways
package leetcode
func NumDecodings(s string) int {
if s[0] == '0' {
return 0
}
dp := make([]int, len(s), len(s))
dp[0] = 1
//dp[i] = dp[i-1] + dp[i-2]
for i := 1; i < len(s); i++ {
if s[i] == '0' {
if s[i-1] == '1' || s[i-1] == '2' {
if i-2 < 0 {
dp[i] = 1
} else {
dp[i] = dp[i-2]
}
} else {
return 0
}
continue
}
if s[i-1] == '1' || (s[i-1] == '2' && s[i] <= '6') {
if i-2 < 0 {
dp[i] = dp[i-1] + 1
} else {
dp[i] = dp[i-1] + dp[i-2]
}
continue
}
dp[i] = dp[i-1]
}
return dp[len(s)-1]
}
