摘要：
1. Use TreeMap since it's keySet is sorted. 阅读全文
摘要：
1. This binary search is find the insertion position. Since it starts from end of array. So it must be greater and equal to mid number. The merge sort 阅读全文
摘要：
1. Add " " to ensure the comparision works. Or add a condition that result.length() > 0 2. character counting decrease happens before check it has bee 阅读全文
摘要：
Basic idea: 1. starting from each element expanding to all map. Find a 0, add one to reach, and level traversal to. 2. Go through each element again. 阅读全文
摘要：
1. Do not forget to left shift the number. 阅读全文
摘要：
1. Do not need to check boundary case since the helper function can add "" into result. 2. Do not forget to add that character if not counting into ab 阅读全文
摘要：
1. When divide k into two parts, it could be 0 for the any part. So i <= nums1.length. 阅读全文