fix readme, update progress

Author: yennanliu

README.md

@@ -1092,7 +1092,7 @@
 823 | [Binary Trees With Factors](https://leetcode.com/problems/binary-trees-with-factors/) |  [Python](./leetcode_python/Dynamic_Programming/binary-trees-with-factors.py)  | _O(n^2)_ | _O(n)_ | Medium |`dp`| AGAIN (not start)
 837 | [New 21 Game](https://leetcode.com/problems/new-21-game/) | [Python](./leetcode_python//Dynamic_Programming/new-21-game.py), [Java](./leetcode_java/src/main/java/LeetCodeJava/DynamicProgramming/New21Game.java)  | _O(n)_ | _O(n)_ | Medium |`dp`, trick, math, `google`| AGAIN (2) (not start)
 838 | [Push Dominoes](https://leetcode.com/problems/push-dominoes/) | [Python](./leetcode_python/Dynamic_Programming/push-dominoes.py)  | _O(n)_ | _O(n)_ | Medium |`dp`,`two pointers`,`google`| AGAIN (not start)
-871 | [Minimum Number of Refueling Stops](https://leetcode.com/problems/minimum-number-of-refueling-stops/editorial/) | [Java](./leetcode_java/src/main/java/LeetCodeJava/DynamicProgramming/MinimumNumberOfRefuelingStops.java)| _O(n)_ | _O(n)_ | Medium |`dp`,`heap`,`google`| AGAIN (not start)
+871 | [Minimum Number of Refueling Stops](https://leetcode.com/problems/minimum-number-of-refueling-stops/editorial/) | [Java](./leetcode_java/src/main/java/LeetCodeJava/DynamicProgramming/MinimumNumberOfRefuelingStops.java)| _O(n)_ | _O(n)_ | Hard |`dp`,`heap`,`google`| AGAIN (not start)
 877 | [Stone Game](https://leetcode.com/problems/stone-game/) | [Python](./leetcode_python/Dynamic_Programming/stone-game.py) | _O(n^2)_ | _O(n)_ | Medium | variant of [Predict the Winner](https://leetcode.com/problems/predict-the-winner/) |  AGAIN (not start)
 926| [Flip String to Monotone Increasing](https://leetcode.com/problems/flip-string-to-monotone-increasing/) | [Python](./leetcode_python/Dynamic_Programming/flip-string-to-monotone-increasing.py) | _O(n)_ | _O(1)_ | Medium |good trick, dp, prefix sum, `google`, `amazon`| AGAIN********** (4)
 931| [Minimum Falling Path Sum](https://leetcode.com/problems/minimum-falling-path-sum/) | [Python](./leetcode_python/Dynamic_Programming/minimum-falling-path-sum.py) | _O(n^2)_ | _O(1)_ | Medium |`google`, `goldman sachs`| AGAIN (not start)

data/progress.md

@@ -1,5 +1,8 @@
 # Progress
 
+# 2024-12-21
+- https://github.com/yennanliu/CS_basics/blob/master/doc/Leetcode_company_frequency-master/Google%206months-%20LeetCode.pdf
+
 # 2024-12-20
 - https://github.com/yennanliu/CS_basics/blob/master/doc/Leetcode_company_frequency-master/Google%206months-%20LeetCode.pdf
 

data/progress.txt

@@ -1,3 +1,4 @@
+20241221:
 20241220: 815,871,593,1109
 20241214: 560,523
 20241208: 304,853,325