complete 3Sum.py

Author: yangdi

src2/3Sum/3Sum.py

@@ -0,0 +1,66 @@
+
+'''
+Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0? 
+Find all unique triplets in the array which gives the sum of zero.
+
+Note:
+Elements in a triplet (a,b,c) must be in non-descending order. (ie, a <= b <= c)
+
+The solution set must not contain duplicate triplets.
+    For example, given array S = {-1 0 1 2 -1 -4},
+
+    A solution set is:
+    (-1, 0, 1)
+    (-1, -1, 2)
+
+'''
+def binary_search(array, value):
+	low, high = 0, len(array)
+	while low < high:
+		mid = (low + high) / 2
+		midval = array[mid]
+		if midval < value:
+			low = mid+1
+		elif midval > value:
+			high = mid
+		else:
+			return mid
+
+	return None
+
+class Solution:
+    # @return a list of lists of length 3, [[val1,val2,val3]]\
+    def threeSum(self, num):
+    	mapping = []
+    	num.sort()
+    	numLen = len(num)
+
+    	for i in range(numLen):
+    		if num[i] == num[i-1] and i != 0:
+    			continue
+    		if num[i] > 0:
+    			break
+
+    		for j in range(i + 1, numLen):
+    			j = numLen + i - j
+
+    			if j + 1 != numLen and num[j] == num[j+1]:
+    				continue
+
+    			needed = 0-num[i]-num[j]
+    			if needed < num[i]:
+    				continue
+    			if needed > num[j]:
+    				break 
+
+    			if binary_search(num[i+1:j], needed) != None: 
+    				mapping.append([num[i], needed, num[j]])
+
+        return mapping
+
+
+if __name__ == '__main__':
+	rst = Solution().threeSum([-2, -1, 0, 1, 2, 3])
+	rst.sort()
+	print rst
+	print Solution().threeSum([])