added SR Latch module

DIRECTORY.md

@@ -117,6 +117,7 @@
   * [Not Gate](boolean_algebra/not_gate.py)
   * [Or Gate](boolean_algebra/or_gate.py)
   * [Quine Mc Cluskey](boolean_algebra/quine_mc_cluskey.py)
+  * [Sr Latch](boolean_algebra/sr_latch.py)
   * [Xnor Gate](boolean_algebra/xnor_gate.py)
   * [Xor Gate](boolean_algebra/xor_gate.py)
 
@@ -425,6 +426,7 @@
   * [Climbing Stairs](dynamic_programming/climbing_stairs.py)
   * [Combination Sum Iv](dynamic_programming/combination_sum_iv.py)
   * [Edit Distance](dynamic_programming/edit_distance.py)
+  * [Egg Dropping](dynamic_programming/egg_dropping.py)
   * [Factorial](dynamic_programming/factorial.py)
   * [Fast Fibonacci](dynamic_programming/fast_fibonacci.py)
   * [Fibonacci](dynamic_programming/fibonacci.py)
@@ -591,6 +593,7 @@
   * [Graphs Floyd Warshall](graphs/graphs_floyd_warshall.py)
   * [Greedy Best First](graphs/greedy_best_first.py)
   * [Greedy Min Vertex Cover](graphs/greedy_min_vertex_cover.py)
+  * [Hopcroft Karp](graphs/hopcroft_karp.py)
   * [Johnson](graphs/johnson.py)
   * [Kahns Algorithm Long](graphs/kahns_algorithm_long.py)
   * [Kahns Algorithm Topo](graphs/kahns_algorithm_topo.py)

boolean_algebra/sr_latch.py

@@ -0,0 +1,51 @@
+"""
+SR latch (this is a cross-coupled NOR implementation;
+for a cross-coupled NAND, just complement the inputs before applying them):
+is a simple memory element that stores 1 bit of information
+State table:
+   | Input 1(set pin) | Input 2(reset pin) | q  (not q) |
+   |       0          |         0          | no change  |
+   |       0          |         1          | 0     1    |
+   |       1          |         0          | 1     0    |
+   |       1          |         1          | undefined  |
+Note: get_current_state() return value of [q,!q]
+"""
+
+
+class SrLatch:
+    """
+    Example:
+    >>> sr_latch = SrLatch(True)
+    >>> sr_latch.get_current_state()
+    [True, False]
+    >>> sr_latch.set_current_state(False,True)
+    >>> sr_latch.get_current_state()
+    [False, True]
+    >>> sr_latch.set_current_state(False,False)
+    >>> sr_latch.get_current_state()
+    [False, True]
+    >>> sr_latch.set_current_state(True,True)
+    Traceback (most recent call last):
+       ...
+    ValueError: undefined state.
+    """
+
+    def __init__(self, initial_state: bool) -> None:
+        self.__initial_state = initial_state
+
+    def get_current_state(self) -> list:
+        return [self.__initial_state, not self.__initial_state]
+
+    def set_current_state(self, set_pin: bool, reset_pin: bool) -> None:
+        if set_pin and reset_pin:
+            raise ValueError("undefined state.")
+        elif not set_pin and reset_pin:
+            self.__initial_state = False
+        elif set_pin and not reset_pin:
+            self.__initial_state = True
+
+
+if __name__ == "__main__":
+    from doctest import testmod
+
+    testmod()