Merge pull request AllAlgorithms#23 from beingadityak/greedy_algos

abranhe · web-flow · commit b89ac274e739 · 2018-10-04T00:13:06.000-04:00
3 Greedy Algorithms in Python
diff --git a/greedy/coin_change.py b/greedy/coin_change.py
@@ -0,0 +1,37 @@
+#!/usr/bin/env python3
+
+"""
+Coin Change implementation in Python (Greedy Method)
+"""
+
+__author__ = "Aditya Krishnakumar"
+
+def minimum_coins(value, denominations):
+    result = []
+    # Assuming denominations is sorted in descendig order
+    for cur_denom in denominations:
+        while cur_denom <= value:
+            result.append(cur_denom)
+            value = value - cur_denom
+
+    return result
+
+# Testing
+def test():
+    scenarios = [[100, [50, 25, 10, 5, 1],      [50, 50]],
+                 [101, [50, 25, 10, 5, 1],      [50, 50, 1]],
+                 [77,  [50, 25, 10, 5, 1],      [50, 25, 1, 1]],
+                 [38,  [50, 25, 10, 5, 1],      [25, 10, 1, 1, 1]],
+                 [17,  [50, 25, 10, 5, 1],      [10, 5, 1, 1]],
+                 [3,   [50, 25, 10, 5, 1],      [1, 1, 1]],
+                 [191, [100, 50, 25, 10, 5, 1], [100, 50, 25, 10, 5, 1]]]
+
+    for scenario in scenarios:
+        actual = minimum_coins(scenario[0], scenario[1])
+        if actual != scenario[2]:
+            message = "Test Failed: Value: {}, Denominations: {}, Expected Result: {}, Actual Result: {}".format(scenario[0], scenario[1], scenario[2], actual)
+            print message
+
+    return None
+
+test()
diff --git a/greedy/dijkstra_algo.py b/greedy/dijkstra_algo.py
@@ -0,0 +1,37 @@
+#!/usr/bin/env python3
+
+"""
+Dijkstra's Algorithm implementation in Python
+"""
+
+__author__ = "Aditya Krishnakumar"
+
+def dijkstra(graph, source):
+
+    vertices, edges = graph
+    dist = dict()
+    previous = dict()
+
+    for vertex in vertices:
+        dist[vertex] = float("inf")
+        previous[vertex] = None
+
+    dist[source] = 0
+    Q = set(vertices)
+
+    while len(Q) > 0:
+        u = minimum_distance(dist, Q)
+        print('Currently considering', u, 'with a distance of', dist[u])
+        Q.remove(u)
+
+        if dist[u] == float('inf'):
+            break
+
+        n = get_neighbours(graph, u)
+        for vertex in n:
+            alt = dist[u] + dist_between(graph, u, vertex)
+            if alt < dist[vertex]:
+                dist[vertex] = alt
+                previous[vertex] = u
+
+    return previous
diff --git a/greedy/fractional_knapsack.py b/greedy/fractional_knapsack.py
@@ -0,0 +1,61 @@
+#!/usr/bin/env python3
+
+"""
+Implementation of Fractional Knapsack Algorithm in Python
+"""
+
+__author__ = "Aditya Krishnakumar"
+
+# Item class with weight and values
+class Item:
+
+	# intialize weight and values
+	def __init__(self, weight=0, value=0):
+
+		self.weight = weight
+		self.value = value
+
+		return
+
+
+def fractional_knapsack(items, W):
+
+	# Sorting items by value /weight
+	sorted(items, key = lambda item: float(item.value)/float(item.weight))
+
+	finalValue = 0.0
+	currentWeight = 0
+
+
+	for item in items:
+
+		if currentWeight + item.weight <= W :
+			# If adding Item won't overflow, add it completely
+			finalValue += item.value
+			currentWeight += item.weight
+
+		else:
+			#If we can't add current Item, add a fraction of it
+			remaining = W - currentWeight
+			finalValue += item.value*(float(remaining)/float(item.weight))
+			break
+
+	return finalValue
+
+def main():
+
+	W = 50
+
+	items = [
+	Item(10, 60),
+	Item(20, 100),
+	Item(30, 120)
+	]
+
+	print("Maximum value we can obtain -{}".format(fractional_knapsack(items, W)))
+
+	return
+
+if __name__ == "__main__":
+
+	main()
