rust_test/src/main.rs

mod tree;
use std::rc::Rc;
use std::cell::RefCell;
use std::collections::HashMap;
use tree::{TreeNode, build_tree};

struct Solution;

impl Solution {
    fn dfs(root: Option<Rc<RefCell<TreeNode>>>, target: i64) -> (HashMap<i64,i32>,i32) {
        if root.is_none() {
            return (HashMap::new(),0);
        }
        let node = root.unwrap();
        let val = node.borrow().val;
        let val = val as i64;
        let mut ans = if val == target { 1 } else { 0 };
        let (left,left_ans) = Self::dfs(node.borrow().left.clone(), target);
        let (right, right_ans) = Self::dfs(node.borrow().right.clone(), target);
        ans += left_ans + right_ans;
        ans += *left.get(&(target - val)).unwrap_or(&0);
        ans += *right.get(&(target - val)).unwrap_or(&0);
        let mut map = HashMap::new();
        map.insert(val, 1);
        for (k,v) in left.iter().chain(right.iter()) {
            *map.entry(k + val).or_insert(0) += v;
        }
        (map,ans)
    }
    pub fn path_sum(root: Option<Rc<RefCell<TreeNode>>>, target_sum: i32) -> i32 {
        let (_,ans) = Self::dfs(root, target_sum as i64);
        ans
    }
}

fn main() {
    let vals = vec![
        Some(10), Some(5), Some(-3), Some(3), Some(2), None, Some(11),
        Some(3), Some(-2), None, Some(1)
    ];
    let root = build_tree(&vals);
    let sl = Solution::path_sum(root, 8);
    println!("{:?}", sl);
}