Rewrite combination_sum.py to python from Java

Author: yangroro

dp/combination_sum.py

@@ -1,4 +1,7 @@
-Given an integer array with all positive numbers and no duplicates, find the number of possible combinations that add up to a positive integer target.
+"""
+Given an integer array with all positive numbers and no duplicates,
+find the number of possible combinations that
+add up to a positive integer target.
 
 Example:
 
@@ -22,42 +25,42 @@
 How does it change the problem?
 What limitation we need to add to the question to allow negative numbers?
 
+"""
 
-private int[] dp;
-
-public int combinationSum4(int[] nums, int target) {
-    dp = new int[target + 1];
-    Arrays.fill(dp, -1);
-    dp[0] = 1;
-    return helper(nums, target);
-}
-
-private int helper(int[] nums, int target) {
-    if (dp[target] != -1) {
-        return dp[target];
-    }
-    int res = 0;
-    for (int i = 0; i < nums.length; i++) {
-        if (target >= nums[i]) {
-            res += helper(nums, target - nums[i]);
-        }
-    }
-    dp[target] = res;
-    return res;
-}
-
-
-EDIT: The above solution is top-down. How about a bottom-up one?
-
-public int combinationSum4(int[] nums, int target) {
-    int[] comb = new int[target + 1];
-    comb[0] = 1;
-    for (int i = 1; i < comb.length; i++) {
-        for (int j = 0; j < nums.length; j++) {
-            if (i - nums[j] >= 0) {
-                comb[i] += comb[i - nums[j]];
-            }
-        }
-    }
-    return comb[target];
-}
+dp = None
+
+
+def helper_topdown(nums, target):
+    global dp
+    if dp[target] != -1:
+        return dp[target]
+    res = 0
+    for i in range(0, len(nums)):
+        if target >= nums[i]:
+            res += helper_topdown(nums, target - nums[i])
+    dp[target] = res
+    return res
+
+
+def combination_sum_topdown(nums, target):
+    global dp
+    dp = [-1] * (target + 1)
+    dp[0] = 1
+    return helper_topdown(nums, target)
+
+
+# EDIT: The above solution is top-down. How about a bottom-up one?
+def combination_sum_bottom_up(nums, target):
+    comb = [0] * (target + 1)
+    comb[0] = 1
+    for i in range(0, len(comb)):
+        for j in range(len(nums)):
+            if i - nums[j] >= 0:
+                comb[i] += comb[i - nums[j]]
+    return comb[target]
+
+
+combination_sum_topdown([1, 2, 3], 4)
+print dp[4]
+
+print combination_sum_bottom_up([1, 2, 3], 4)