摘要：
https://leetcode.com/problems/accounts-merge/description/ 阅读全文
摘要：
Use array. Use map. 阅读全文
摘要：
https://leetcode.com/problems/friend-circles/description/ 阅读全文
摘要：
https://leetcode.com/problems/number-of-islands/description/ 阅读全文
摘要：
https://leetcode.com/problems/redundant-connection/description/ Use map to do Union Find. 阅读全文
摘要：
https://leetcode.com/problems/sort-characters-by-frequency/description/ 阅读全文
摘要：
https://leetcode.com/problems/non-overlapping-intervals/description/ Greedy. Sort by (start,-end). Scan from left to right, if we see 2 intervals over 阅读全文
摘要：
When we see ordering, consider stack. When we process item one by one, but I can't process current item, we move to next item (and that item might dep 阅读全文
摘要：
https://leetcode.com/problems/next-greater-element-ii/description/ 阅读全文
摘要：
https://leetcode.com/problems/next-greater-element-i/description/ 阅读全文