97% speed, n*m complexity
Intuition\n Describe your first thoughts on how to solve this problem. \n\n# Approach\n Describe your approach to solving the problem. \n\n# Complexity\n- Time 
# Intuition\n<!-- Describe your first thoughts on how to solve this problem. -->\n\n# Approach\n<!-- Describe your approach to solving the problem. -->\n\n# Complexity\n- Time complexity:\n<!-- Add your time complexity here, e.g. $$O(n)$$ -->\n\n- Space complexity:\n<!-- Add your space complexity here, e.g. $$O(n)$$ -->\n\n# Code\n```python3 []\nclass Solution:\n    def minDeletionSize(self, strs: List[str]) -> int:\n        cnt=0\n        prev_s=set([i for i in range(len(strs))])\n        for j in range(len(strs[0])):\n            flag=0\n            s=set()\n            for i in range(1,len(strs)):\n                if i-1 not in prev_s:\n                    continue\n                if strs[i][j]<strs[i-1][j]:\n                    cnt+=1\n                    break\n                elif strs[i][j]==strs[i-1][j]:\n                    s.add(i-1)\n                    flag=1\n            else: \n                if not flag: return cnt\n                prev_s=s\n        return cnt\n```
['Python3']