add binary_search_st

Author: shellfly

algs4/binary_search_st.py

@@ -0,0 +1,95 @@
+"""
+ *  Execution:    python binary_search_st
+ *  Data files:   https://algs4.cs.princeton.edu/31elementary/tinyST.txt  
+ *  
+ *  Symbol table implementation with binary search in an ordered array.
+ *
+ *  % more tinyST.txt
+ *  S E A R C H E X A M P L E
+ *  
+ *  % python binary_search_st < tinyST.txt
+ *  C 4
+ *  E 12
+ *  H 5
+ *  L 11
+ *  M 9
+ *  P 10
+ *  R 3
+ *  S 0
+ *  X 7
+ *
+ """
+
+
+class BinarySearchST:
+    init_capacity = 2
+
+    def __init__(self):
+        self.keys = [None]*self.init_capacity
+        self.vals = [None]*self.init_capacity
+        self.n = 0
+
+    def rank(self, arr, key):
+        lo, hi = 0, self.n - 1
+        while lo <= hi:
+            mid = lo + (hi - lo) // 2
+            if (key < arr[mid]):
+                hi = mid - 1
+            elif (key > arr[mid]):
+                lo = mid + 1
+            else:
+                return mid
+        return lo
+
+    def resize(self, capacity):
+        self.keys = self.keys + [None]*(capacity-len(self.keys))
+        self.vals = self.vals + [None]*(capacity-len(self.vals))
+
+    def contains(self, key):
+        return self.get(key) != None
+
+    def get(self, key):
+        i = self.rank(self.keys, key)
+        if i < self.n and self.keys[i] == key:
+            return self.vals[i]
+        return None
+
+    def put(self, key, val):
+        i = self.rank(self.keys, key)
+        if i < self.n and self.keys[i] == key:
+            self.vals[i] = val
+            return
+
+        if self.n == len(self.keys):
+            self.resize(self.n*2)
+
+        j = self.n
+        while j > i:
+            self.keys[j], self.vals[j] = self.keys[j-1], self.vals[j-1]
+            j -= 1
+        self.keys[i], self.vals[i] = key, val
+        self.n += 1
+
+    def delete(self, key):
+        self.put(key, None)
+
+    def is_empty(self):
+        return self.n == 0
+
+    def Size(self):
+        return self.n
+
+    def Keys(self):
+        return self.keys[:self.n]
+
+
+if __name__ == '__main__':
+    import sys
+    st = BinarySearchST()
+    i = 0
+    for line in sys.stdin:
+        for key in line.split():
+            st.put(key, i)
+            i += 1
+    for s in st.Keys():
+        print(s + " " + str(st.get(s)))