113 Path Sum II

Author: int32bit

algorithms/PathSum/README.md

@@ -36,3 +36,7 @@ bool hasPathSum(struct TreeNode *root, int sum) {
 	return true;
 }
 ```
+
+## 扩展
+
+见[Path Sum II](../PathSum2).

algorithms/PathSum2/README.md

@@ -0,0 +1,47 @@
+## Path Sum II
+
+Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum.
+
+For example:
+Given the below binary tree and `sum = 22`,
+```
+              5
+             / \
+            4   8
+           /   / \
+          11  13  4
+         /  \    / \
+        7    2  5   1
+```
+return
+```
+[
+   [5,4,11,2],
+   [5,8,4,5]
+]
+```
+
+这题和[Path Sum I](../PathSum)一样使用前序遍历的方法，不过遍历的同时需要保存当前的值。
+
+设当前访问的节点为p，已访问的节点保存于cur, 结果集result, 目标值sum
+
+* 若p是空节点，直接返回
+* p值压入cur，`sum -= p->val`
+* 若p是叶子节点，并且`sum == 0`, 把cur压入result结果集中
+* 否则p不是叶子节点，递归探测左孩子、右孩子.
+
+## Code
+```cpp
+void pathSum(vector<vector<int>> &result, vector<int> cur, TreeNode *root, int sum) {
+    if (root == NULL)
+	    return;
+    cur.push_back(root->val);
+    sum -= root->val;
+    if (isLeft(root) && sum == 0) {
+	    result.push_back(cur);
+	    return;
+    }
+    pathSum(result, cur, root->left, sum);
+    pathSum(result, cur, root->right, sum);
+}
+```

algorithms/PathSum2/solve.cpp

@@ -0,0 +1,69 @@
+#include <vector>
+#include <iostream>
+#include <algorithm>
+using namespace std;
+struct TreeNode {
+    int val;
+    TreeNode *left;
+    TreeNode *right;
+    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+};
+class Solution {
+public:
+    vector<vector<int> > pathSum(TreeNode *root, int sum) {
+	    vector<vector<int>> result;
+	    vector<int> t;
+	    pathSum(result, t, root, sum);
+	    return result;
+    }
+private:
+    void pathSum(vector<vector<int>> &result, vector<int> cur, TreeNode *root, int sum) {
+	    if (root == NULL)
+		    return;
+	    cur.push_back(root->val);
+	    sum -= root->val;
+	    if (isLeft(root) && sum == 0) {
+		    result.push_back(cur);
+		    return;
+	    }
+	    pathSum(result, cur, root->left, sum);
+	    pathSum(result, cur, root->right, sum);
+    }
+    bool isLeft(TreeNode *p) {
+	    if (p == nullptr)
+		    return false;
+	    return p->left == nullptr && p->right == nullptr;
+    }
+};
+TreeNode *mk_node(int val)
+{
+	TreeNode *p = new TreeNode(val);
+	return p;
+}
+void mk_child(TreeNode *root, TreeNode *left, TreeNode *right)
+{
+	root->left = left;
+	root->right = right;
+}
+void mk_child(TreeNode *root, int left, int right)
+{
+	mk_child(root, mk_node(left), mk_node(right));
+}
+int main(int argc, char **argv)
+{
+	Solution solution;
+	TreeNode *root = mk_node(5);
+	mk_child(root, 4, 8);
+	TreeNode *left = root->left;
+	TreeNode *right = root->right;
+	mk_child(left, mk_node(11), nullptr);
+	mk_child(left->left, 7, 2);
+	mk_child(right, 13, 4);
+	mk_child(right->right, 5, 1);
+	auto result = solution.pathSum(root, 22);
+	cout << "size: " << result.size() << endl;
+	for (auto v : result) {
+		for_each(v.begin(), v.end(), [](int i){cout << i << " ";});
+		cout << endl;
+	}
+}