数组num[5] = {1, 2, 3, 4, 5};调用next_permutation(num, num + 5),使数组num内的数据排列变为一个序列(每次调用该序列字典序从小到大) prev_permutation函数的作用和next_permutation函数作用相反
num[5] = {1, 2, 3, 4, 5};
next_permutation(num, num + 5)
num
prev_permutation
next_permutation