Next Permutation

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本文介绍了一个用于重新排列数字数组以获得下一个更大排列的算法。如果无法找到更大的排列，则将其排列为最小可能的顺序（即升序）。算法在原地进行操作，不使用额外内存。

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Implement next permutation, which rearranges numbers into the lexicographically next greater permutation of numbers.

If such arrangement is not possible, it must rearrange it as the lowest possible order (ie, sorted in ascending order).

The replacement must be in-place, do not allocate extra memory.

Here are some examples. Inputs are in the left-hand column and its corresponding outputs are in the right-hand column.
1,2,3 → 1,3,2
3,2,1 → 1,2,3
1,1,5 → 1,5,1

class Solution:
    # @param num_copy, a list of integer
    # @return a list of integer
    def nextPermutation(self, num):
        num_copy=num[:]
        if len(num_copy)<=1:
            return num_copy
           
        #right to left ,find partition index
        partition_index = -1
        for i in range(len(num_copy)-2,-1,-1):
            if num_copy[i] < num_copy[i+1]:
                partition_index=i
                break
        #could not find
        if partition_index==-1:
            num_copy.reverse()
            return num_copy
        #right to left ,find change index
        change_index=-1
        for i in range(len(num_copy)-1,-1,-1):
            if num_copy[i] > num_copy[partition_index]:
                change_index=i
                break
        #swap
        num_copy[partition_index],num_copy[change_index]=num_copy[change_index],num_copy[partition_index]
        num_copy[partition_index+1:] = reversed(num_copy[partition_index+1:])
        return num_copy