[LEET-437] add 437

fishercoder1534 · fishercoder1534 · commit 4899abe42309 · 2017-02-27T08:43:50.000-08:00
diff --git a/leetcode-algorithms/README.md b/leetcode-algorithms/README.md
@@ -40,6 +40,7 @@
 |442|[Find All Duplicates in an Array](https://leetcode.com/problems/find-all-duplicates-in-an-array/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/FindAllDuplicatesinanArray.java)| O(n)|O(1) | Medium| Array
 |441|[Arranging Coins](https://leetcode.com/problems/arrange-coins/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/ArrangingCoins.java)| O(n)|O(1) | Easy|
 |438|[Find All Anagrams in a String](https://leetcode.com/problems/find-all-anagrams-in-a-string/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/FindAllAnagramsinaString.java)| O(n)|O(1) | Easy|
+|437|[Path Sum III](https://leetcode.com/problems/path-sum-iii/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/PathSumIII.java) | O(n^2) |O(n) | Easy| DFS, recursion
 |436|[Find Right Interval](https://leetcode.com/problems/find-right-interval/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/FindRightInterval.java) | O(nlogn) |O(n) | Medium| Binary Search
 |435|[Non-overlapping Intervals](https://leetcode.com/problems/non-overlapping-intervals/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/NonOverlappingIntervals.java) | O(nlogn) |O(1) | Medium| Greedy
 |434|[Number of Segments in a String](https://leetcode.com/problems/number-of-segments-in-a-string/)|[Solution](../../master/leetcode-algorithms/src/main/java/com/stevesun/solutions/NumberofSegmentsinaString.java)| O(n)|O(1) | Easy|
diff --git a/leetcode-algorithms/src/main/java/com/stevesun/solutions/PathSumIII.java b/leetcode-algorithms/src/main/java/com/stevesun/solutions/PathSumIII.java
@@ -0,0 +1,44 @@
+package com.stevesun.solutions;
+
+import com.stevesun.common.classes.TreeNode;
+
+/**
+ * You are given a binary tree in which each node contains an integer value.
+
+ Find the number of paths that sum to a given value.
+
+ The path does not need to start or end at the root or a leaf, but it must go downwards (traveling only from parent nodes to child nodes).
+
+ The tree has no more than 1,000 nodes and the values are in the range -1,000,000 to 1,000,000.
+
+ Example:
+
+ root = [10,5,-3,3,2,null,11,3,-2,null,1], sum = 8
+
+      10
+     /  \
+    5   -3
+   / \    \
+  3   2   11
+ / \   \
+3  -2  1
+
+ Return 3. The paths that sum to 8 are:
+
+ 1.  5 -> 3
+ 2.  5 -> 2 -> 1
+ 3. -3 -> 11
+ */
+public class PathSumIII {
+
+    public int pathSum(TreeNode root, int sum) {
+        if (root == null) return 0;
+        return pathSumFrom(root, sum) + pathSum(root.left, sum) + pathSum(root.right, sum);
+    }
+
+    private int pathSumFrom(TreeNode root, int sum) {
+        if (root == null) return 0;
+        return (root.val == sum ? 1 : 0) + pathSumFrom(root.left, sum - root.val) + pathSumFrom(root.right, sum - root.val);
+    }
+
+}
