Split Array into Consecutive Subsequences 解法
2017-10-26 12:12
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Split Array into Consecutive Subsequences 解法
第七周题目难度:Media
LeetCode题号:659
题目
Description:
You are given an integer array sorted in ascending order (may contain duplicates), you need to split them into several subsequences, where each subsequences consist of at least 3 consecutive integers. Return whether you can make such a split.Example1:
Input: [1,2,3,3,4,5]
Output: True
Explanation:
You can split them into two consecutive subsequences :
1, 2, 3
3, 4, 5
Example2:
Input: [1,2,3,3,4,4,5,5]
Output: True
Explanation:
You can split them into two consecutive subsequences :
1, 2, 3, 4, 5
3, 4, 5
Example3:
Input: [1,2,3,4,4,5]
Output: False
思考
进行两次遍历,第一次找出每个数字出现的频率,第二次切割子串。通过unordered_map来处理,声明count用来保存数字 i 出现频率,tail用来保存以数字 i 结尾的子串的个数。
第二次循环遍历时,首先判断这个数“i”是否还已经被切割完了
若还在,向后判断他的后一个数是否是结束符,如果是,则后一个数tail值减一,当前数的tail值加一;
如果后一个数不是结束符,说明在他前面当前这个数不能并如果前面的串了,要向后发展。
判断后两个数是否存在,存在的话就抽取了后两个数(让他们的count值减一),然后让第三个数的tail值加一
如果以上情况都不存在,则说明如果构成符合题意的子串,返回false
代码
class Solution { public: bool isPossible(vector<int>& nums) { unordered_map<int, int> tail, count; for (int &i : nums) { count[i]++; } for (int &i : nums) { if (!count[i]) { continue; } count[i]--; if (tail[i-1] > 0) { tail[i-1]--; tail[i]++; } else if (count[i+1] && count[i+2]) { tail[i+2]++; count[i+1]--; count[i+2]--; } else { return false; } } return true; } };
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