标签：some algo last class think ref ESS AMM UNC
For example we have
‘a‘ -> 1
‘b‘ -> 2
..
‘z‘ -> 26
By given "12", we can decode the string to give result "ab" or ‘L‘, 2 ways to decode, your function should return 2 as an answer.
Now asking by given "1246", what should be the return number;
The thinking process is somehow like this:
by given "1" -> we got ‘a‘
by given "" -> we got ""
by given "12345" -> ‘a‘ + decode(‘2345‘) or ‘L‘ + decode(‘345‘), therefore number of ways to decode "12345"is the same of decode(2345)+decode(345).
Somehow we can see that this is a recursion task, therefore we can use Dynamice Programming + memo way to solve the problem.
const data = "1246"; function num_ways(data) { // k : count from last to beginning function helper(data, k) { if (k === 0) { // if k equals 0, mean only one single digital number left // means there must be one char return 1; } if (data === "") { // if data equals empty, then return 1 return 1; } if (memo[k] != null) { return memo[k]; } const start = data.length - k; if (data[start] === "0") { // if sth start as 0, then no char return 0; } let result = helper(data, k - 1); if (k >= 2 && parseInt(data.slice(start, start + 2), 10) <= 26) { result += helper(data, k - 2); } memo[k] = result; return result; } let memo = []; return helper(data, data.length, memo); } const res = num_ways(data); console.log(res);
[Algorithm -- Dynamic programming] How Many Ways to Decode This Message?
标签：some algo last class think ref ESS AMM UNC
原文地址：https://www.cnblogs.com/Answer1215/p/10468653.html
