solved q437

Author: ruislan

src/q/mod.rs

@@ -224,6 +224,7 @@ mod q423;
 mod q424;
 mod q434;
 mod q435;
+mod q437;
 mod q441;
 mod q442;
 mod q443;

src/q/q437.rs

@@ -0,0 +1,52 @@
+use std::cell::RefCell;
+use std::rc::Rc;
+
+use crate::q::Solution;
+
+#[derive(Debug, PartialEq, Eq)]
+pub struct TreeNode {
+    pub val: i32,
+    pub left: Option<Rc<RefCell<TreeNode>>>,
+    pub right: Option<Rc<RefCell<TreeNode>>>,
+}
+
+#[allow(unused)]
+impl TreeNode {
+    #[inline]
+    pub fn new(val: i32) -> Self {
+        TreeNode {
+            val,
+            left: None,
+            right: None,
+        }
+    }
+}
+
+#[allow(unused)]
+impl Solution {
+    pub fn path_sum(root: Option<Rc<RefCell<TreeNode>>>, target_sum: i32) -> i32 {
+        // 方法1
+        // dfs
+        // 每次向下我们都将结果增加1位，然后遍历，如果结果正好等于target，就叠加计数
+        // AC 0ms 2.2mb 126/126
+        fn dfs(node: Option<Rc<RefCell<TreeNode>>>, target: i32, path: &mut Vec<i32>) -> i32 {
+            if let Some(node) = node {
+                let left = node.borrow_mut().left.take();
+                let right = node.borrow_mut().right.take();
+                let val = node.borrow().val;
+                path.iter_mut().for_each(|x| *x += val);
+                path.push(val);
+                let count = path.iter().filter(|&&x| x == target).count() as i32;
+
+                let left_count = dfs(left, target, path);
+                let right_count = dfs(right, target, path);
+
+                path.pop();
+                path.iter_mut().for_each(|x| *x -= val);
+                return left_count + right_count + count;
+            }
+            0
+        }
+        dfs(root, target_sum, &mut Vec::new())
+    }
+}