leetcode练习:38. Count and Say
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The count-and-say sequence is the sequence of integers with the first five terms as following:
1. 1 2. 11 3. 21 4. 1211 5. 111221
1
is read off as "one 1"
or 11
.11
is read off as "two 1s"
or 21
.21
is read off as "one 2
, then one 1"
or 1211
.
Given an integer n, generate the nth term of the count-and-say sequence.
Note: Each term of the sequence of integers will be represented as a string.
Example 1:
Input: 1 Output: "1"
Example 2:
Input: 4 Output: "1211"
这个题目,一开始还真的没看懂~后来上网翻译了一下发现意思就是,数有几个1,几个2,这样,后面一个数前面一个,所以很明显就可以用递归做,当然所有的递归都可以用迭代写出来咯。
var countAndSay = function(n) { if(n==1) return "1"; var last = countAndSay(n-1); var len = last.length; var num = 1; var res = ""; for(var i=1;i<=len;i++){ if(last[i] == last[i-1]){ num++; } else { res = res + num + last[i-1]; num = 1; } } return res; };
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