124. 二叉树中的最大路径和

src/main.rs

@@ -1,24 +1,30 @@
 mod arr;
+mod tree;
+
+use crate::tree::{TreeNode, build_tree_from_str};
 struct Solution {}
+use std::cell::RefCell;
+use std::rc::Rc;
 impl Solution {
-    pub fn longest_common_subsequence(text1: String, text2: String) -> i32 {
-        let mut dp = vec![vec![0; text2.len() + 1]; text1.len() + 1];
-        let text1 = text1.chars().collect::<Vec<char>>();
-        let text2 = text2.chars().collect::<Vec<char>>();
-        for i in 0..text1.len() {
-            for j in 0..text2.len() {
-                dp[i + 1][j + 1] = dp[i + 1][j].max(dp[i][j + 1]);
-                if text1[i] == text2[j] {
-                    dp[i + 1][j + 1] = dp[i + 1][j + 1].max(dp[i][j] + 1);
-                }
-            }
+    pub fn max_path_sum(root: Option<Rc<RefCell<TreeNode>>>) -> i32 {
+        let (_,ans) = Self::dfs(&root);
+        ans
+    }
+    fn dfs(root: &Option<Rc<RefCell<TreeNode>>>) -> (i32, i32) {
+        if root.is_none() {
+            return (-100000000, -100000000);
         }
-        dp[text1.len()][text2.len()]
+        let (la, ln) = Self::dfs(&root.as_ref().unwrap().borrow().left);
+        let (ra, rn) = Self::dfs(&root.as_ref().unwrap().borrow().right);
+        let val = root.as_ref().unwrap().borrow().val;
+        let a = val.max(val + la).max(val + ra);
+        let n = a.max(ln).max(rn).max(val + la + ra);
+        (a, n)
     }
 }
 fn main() {
     println!(
         "{:?}",
-        Solution::longest_common_subsequence("abcde".to_string(), "ace".to_string())
+        Solution::max_path_sum(build_tree_from_str("[5,4,8,11,null,13,4,7,2,null,null,null,1]"))
     );
 }

src/tree.rs

@@ -15,7 +15,19 @@ impl TreeNode {
         TreeNode { val, left: None, right: None }
     }
 }
-
+pub fn build_tree_from_str(s: &str) -> Option<Rc<RefCell<TreeNode>>> {
+    // [-10,9,20,null,null,15,7]
+    let s = s.trim_matches(&['[', ']'][..]).split(',').map(|x| x.trim()).collect::<Vec<_>>();
+    let mut vals = vec![];
+    for x in s {
+        if x == "null" {
+            vals.push(None);
+        }else {
+            vals.push(Some(i32::from_str_radix(x, 10).unwrap()));
+        }
+    }
+    build_tree(&vals)
+}
 pub fn build_tree(vals: &[Option<i32>]) -> Option<Rc<RefCell<TreeNode>>> {
     if vals.is_empty() || vals[0].is_none() {
         return None;