对于一组数据是否符合某个分布，有很多种统计检验的方法，比如K-S检验，卡方检验，从图形上我们可以用Q-Q图和P-P图来检查数据是否服从某种分布。他们可以检验的分布图包括：β分布，t分布、卡方分布、伽马分布、正态分布、均匀分...

Given two integers n and k, return all possible combinations of k numbers out of 1 ... n.

Given a set of candidate numbers (candidates) (without duplicates) and a target number (target), find all unique combinations in candidates where the candidate ...

Find all possible combinations of k numbers that add up to a number n, given that only numbers from 1 to 9 can be used and each combination should be a unique s...

Given a collection of numbers that might contain duplicates, return all possible unique permutations.

Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number.

Given a positive integer n, find the least number of perfect square numbers (for example, 1, 4, 9, 16, ...) which sum to n.

Given a m x n grid filled with non-negative numbers, find a path from top left to bottom right which minimizes the sum of all numbers along its path.

82. Remove Duplicates from Sorted List II

抽屉原理又称鸽巢原理：把 n+1个物品放进 n个盒子里，那么至少有一个盒子包含两个及以上的物品。