摘要：
You are given two strings s and t of the same length. You want to change s to t. Changing the i-th character of s to i-th character of t costs |s[i] - 阅读全文
摘要：
Given an array of integers arr, write a function that returns true if and only if the number of occurrences of each value in the array is unique. Exam 阅读全文
