Update README.md

Author: kamyu104

README.md

@@ -1524,7 +1524,7 @@
 1595| [Minimum Cost to Connect Two Groups of Points](https://leetcode.com/problems/minimum-cost-to-connect-two-groups-of-points/)| [C++](./C++/minimum-cost-to-connect-two-groups-of-points.cpp) [Python](./Python/minimum-cost-to-connect-two-groups-of-points.py) | _O(m * n * 2^n)_    | _O(2^n)_          | Hard           ||
 1617| [Count Subtrees With Max Distance Between Cities](https://leetcode.com/problems/count-subtrees-with-max-distance-between-cities/)| [C++](./C++/count-subtrees-with-max-distance-between-cities.cpp) [Python](./Python/count-subtrees-with-max-distance-between-cities.py) | _O(n^6)_    | _O(n^3)_          | Hard           || Backtracking, Graph
 1626| [Best Team With No Conflicts](https://leetcode.com/problems/best-team-with-no-conflicts/)| [C++](./C++/best-team-with-no-conflicts.cpp) [Python](./Python/best-team-with-no-conflicts.py) | _O(nloga)_    | _O(n)_          | Medium           | variant of [Longest Increasing Subsequence](https://leetcode.com/problems/longest-increasing-subsequence/) | Sort, DP, Segment Tree
-1639| [Number of Ways to Form a Target String Given a Dictionary](https://leetcode.com/problems/number-of-ways-to-form-a-target-string-given-a-dictionary/)| [C++](./C++/number-of-ways-to-form-a-target-string-given-a-dictionary.cpp) [Python](./Python/number-of-ways-to-form-a-target-string-given-a-dictionary.py) | _O(l * (w + n))_    | _O(n)_          | Medium           | | 
+1639| [Number of Ways to Form a Target String Given a Dictionary](https://leetcode.com/problems/number-of-ways-to-form-a-target-string-given-a-dictionary/)| [C++](./C++/number-of-ways-to-form-a-target-string-given-a-dictionary.cpp) [Python](./Python/number-of-ways-to-form-a-target-string-given-a-dictionary.py) | _O(l * (w + n))_    | _O(n)_          | Hard           | | 
 
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