Suppose you have a random list of people standing in a queue. Each person is described by a pair of integers (h, k), where h is the height of the person and k is the number of people in front of this person who have a height greater than or equal to h. Write an algorithm to reconstruct the queue.

Note: The number of people is less than 1,100.

Example

Input: [[7,0], [4,4], [7,1], [5,0], [6,1], [5,2]]

Output: [[5,0], [7,0], [5,2], [6,1], [4,4], [7,1]]

Solution(not mine)

Easy concept with Python/C++/Java Solution
Pick out tallest group of people and sort them in a subarray (S). Since there's no other groups of people taller than them, therefore each guy's index will be just as same as his k value.
For 2nd tallest group (and the rest), insert each one of them into (S) by k value. So on and so forth.
E.g.
input: [[7,0], [4,4], [7,1], [5,0], [6,1], [5,2]]
subarray after step 1: [[7,0], [7,1]]
subarray after step 2: [[7,0], [6,1], [7,1]]
...

It's not the most concise code, but I think it well explained the concept.

class Solution(object):
    def reconstructQueue(self, people):
        if not people: return []

        # obtain everyone's info
        # key=height, value=k-value, index in original array
        peopledct, height, res = {}, [], []

        for i in xrange(len(people)):
            p = people[i]
            if p[0] in peopledct:
                peopledct[p[0]] += (p[1], i),
            else:
                peopledct[p[0]] = [(p[1], i)]
                height += p[0],

        height.sort()      # here are different heights we have

        # sort from the tallest group
        for h in height[::-1]:
            peopledct[h].sort()
            for p in peopledct[h]:
                res.insert(p[0], people[p[1]])

        return res