      "## Constraints\n",
      "\n",
      "* Can we assume this is a stack of ints?\n",
      "    * Yes\n",
      "* If we call this function on an empty stack, can we return maxsize?\n",
      "    * Yes\n",
      "* Can we assume we already have a stack class that can be used for this problem?\n",
      "    * Yes"
     ]
    },
 
</s> remove     "* Space: O(n)\n",
 </s> add     "* Space: O(1)\n", </s> remove     "        stack = MyStack()\n",
 </s> add     "        stack = StackMin()\n",
    "* Can we assume the input values for push are valid?\n",
    "    * Yes\n",
    "* If we call this function on an empty stack, can we return sys.maxsize?\n",
      "## Constraints\n",
      "\n",
      "* Can we assume this is a stack of ints?\n",
      "    * Yes\n",
    "* Can we assume the input values for push are valid?\n",
    "    * Yes\n",
    "* If we call this function on an empty stack, can we return sys.maxsize?\n",
      "    * Yes\n",
      "* Can we assume we already have a stack class that can be used for this problem?\n",
      "    * Yes"
     ]
    },
keep keep keep keep replace keep keep keep keep keep
 Polish stack min challenge and solution (#72)

Update constraints, algorithm discussion, code, and tests. 
stacks_queues/stack_min/stack_min_challenge.ipynb