Update closest.py

algorithmic_toolbox/week_4/03_divide_and_conquer_starter_files_20160804/closest/closest.py

@@ -1,17 +1,58 @@
-# Uses python3
+#Uses python3
 import sys
 import math
 
 
-def minimum_distance(x, y):
-    # write your code here
-    return 10 ** 18
+def dist(p1, p2): 
+    return float(math.sqrt((p1[0]- p2[0]) * (p1[0] - p2[0]) +(p1[1] - p2[1]) * (p1[1] - p2[1])) )
 
+def bruteForce(P, n): 
+    min_val = float('inf')  
+    for i in range(n): 
+        for j in range(i + 1, n): 
+            if dist(P[i], P[j]) < min_val: 
+                min_val = dist(P[i], P[j]) 
+
+    return min_val 
+
+def stripClosest(strip, size, d): 
+
+    # Initialize the minimum distance as d  
+    min_val = d  
+
+    strip.sort(key = lambda p:p[1])
+    i=0
+    for x,y in strip: 
+        j = i + 1
+        while j < size and (strip [j][1] - strip[i][1]) < min_val: 
+            min_val = dist(strip[i], strip[j]) 
+            j += 1
+        i+=1
+    return min_val
+
+def closestUtil(X,Y):
+    P=zip(X,Y)
+    P=sorted(P)
+    Y=[y for _, y in P]
+    X=sorted(X)
+    n=len(X)
+    if n <= 3:  
+        return bruteForce(P,len(P))
+    mid = n // 2
+    midPoint = P[mid]
+    dl = closestUtil(X[:mid], Y[:mid]) 
+    dr = closestUtil(X[mid:], Y[mid:]) 
+    d = min(dl, dr)
+    strip=[]
+    for i in range(n):  
+        if abs(X[i] - X[mid]) < d:  
+            strip.append((X[i],Y[i])) 
+    return min(d, stripClosest(strip, len(strip), d))
 
 if __name__ == '__main__':
     input = sys.stdin.read()
     data = list(map(int, input.split()))
     n = data[0]
     x = data[1::2]
     y = data[2::2]
-    print("{0:.9f}".format(minimum_distance(x, y)))
+    print("{0:.9f}".format(closestUtil(x, y)))