leetcode算法题--把数字翻译成字符串

原题链接：https://leetcode.cn/problems/ba-shu-zi-fan-yi-cheng-zi-fu-chuan-lcof/?envType=study-plan-v2&envId=coding-interviews

其实是跳台阶问题，给想复杂了。。

func translateNum(num int) int {
    mp1 := make(map[string]string)
    for i := 0; i < 26; i++ {
        ss := string('a'+i)
        nn := strconv.Itoa(i) 
        mp1[nn]=ss
    }
    mp2 := make(map[string]int)
    s := strconv.Itoa(num)
    n := len(s)
    var dfs func(idx int, str string)
    dfs = func(idx int, str string) {
        if idx == n {
            mp2[str] = 1
            return 
        } 
        for i := idx+1; i <= n; i++ {
            nn := s[idx:i]
            ss, ok := mp1[nn]
            if !ok {
                break
            }
            dfs(i, str+ss) 
        }
    }
    dfs(0, "")
    return len(mp2)
}

优化

func translateNum(num int) int {
    s := strconv.Itoa(num)
    n := len(s)
    if n <= 1 {
        return n 
    }
    dp := make([]int, n)
    dp[0] = 1  
    dp[1] = 1 
    if s[:2] <= "25" && s[:2] >= "10" {
        dp[1] = 2
    }
    for i := 2; i < n; i ++ {
        dp[i] = dp[i-1]
        ss := s[i-1:i+1]
        if ss <= "25" && ss >= "10" {
            dp[i] += dp[i-2]
        } 
    } 
    return dp[n-1] 
}