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.

Note:

You can only move either down or right at any point in time.

Given a linked list, determine if it has a cycle in it.

Follow up:

Space: O(1)

There are N gas stations along a circular route, where the amount of gas at station i is gas[i].

You have a car with an unlimited gas tank and it costs cost[i] of gas to travel from station i to its next station (i+1). You begin the journey with an empty tank at one of the gas stations.

Return the starting gas station’s index if you can travel around the circuit once, otherwise return -1.

Note:

The solution is guaranteed to be unique.

Write a function that takes a string as input and reverse only the vowels of a string.

Example 1:

Given s = “hello”, return “holle”.

Example 2:

Given s = “leetcode”, return “leotcede”.

Note:

The vowels does not include the letter “y”.

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

For example, given n = 12, return 3 because 12 = 4 + 4 + 4; given n = 13, return 2 because 13 = 4 + 9.

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

Given an integer array of size n, find all elements that appear more than ⌊ n/3 ⌋ times. The algorithm should run in linear time and in O(1) space.

Given an array S of n integers, are there elements a, b, c, and d in S such that a + b + c + d = target? Find all unique quadruplets in the array which gives the sum of target.

Note: The solution set must not contain duplicate quadruplets.

Example

Given array S = [1, 0, -1, 0, -2, 2], and target = 0.

A solution set is:

1
2
3
4
5

[
  [-1,  0, 0, 1],
  [-2, -1, 1, 2],
  [-2,  0, 0, 2]
]

Given an integer n, generate a square matrix filled with elements from 1 to n² in spiral order.

Example

Given n = 3,

You should return the following matrix:

1
2
3
4
5

[
 [ 1, 2, 3 ],
 [ 8, 9, 4 ],
 [ 7, 6, 5 ]
]

Given an array of integers and an integer k, find out whether there are two distinct indices i and j in the array such that nums[i] = nums[j] and the difference between i and j is at most k.