add: Path Sum III

Author: sidvishnoi

0437-path-sum-iii.rs

@@ -0,0 +1,41 @@
+mod tree;
+use tree::*;
+struct Solution;
+
+use std::cell::RefCell;
+use std::rc::Rc;
+
+impl Solution {
+    pub fn path_sum(root: Option<Rc<RefCell<TreeNode>>>, sum: i32) -> i32 {
+        if let Some(ref r) = root {
+            Self::path_sum_from(root.clone(), sum)
+                + Self::path_sum(r.borrow().left.clone(), sum)
+                + Self::path_sum(r.borrow().right.clone(), sum)
+        } else {
+            0
+        }
+    }
+
+    fn path_sum_from(root: Option<Rc<RefCell<TreeNode>>>, remaining_sum: i32) -> i32 {
+        if let Some(ref node) = root {
+            let val = node.borrow().val;
+            let path_count = if val == remaining_sum { 1 } else { 0 };
+            path_count
+                + Self::path_sum_from(node.borrow().left.clone(), remaining_sum - val)
+                + Self::path_sum_from(node.borrow().right.clone(), remaining_sum - val)
+        } else {
+            0
+        }
+    }
+}
+
+fn main() {
+    assert_eq!(
+        3,
+        Solution::path_sum(tree![10, 5, -3, 3, 2, null, 11, 3, -2, null, 1], 8)
+    );
+    assert_eq!(
+        2,
+        Solution::path_sum(tree![1, null, 2, null, 3, null, 4, null, 5], 3)
+    );
+}