Create 437-path-sum-iii.js

Author: everthis

437-path-sum-iii.js

@@ -0,0 +1,29 @@
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val) {
+ *     this.val = val;
+ *     this.left = this.right = null;
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @param {number} sum
+ * @return {number}
+ */
+function pathSum(root, sum) {
+    const preSums = new Map([[0, 1]]);
+    let count = 0;
+    visit(root, 0);
+    return count;
+    
+    function visit(node, preSum) {
+        if (!node) return;
+        preSum += node.val;
+        count += preSums.get(preSum - sum) || 0;
+        preSums.set(preSum, (preSums.get(preSum) || 0) + 1);
+        visit(node.left, preSum);
+        visit(node.right, preSum);
+        preSums.set(preSum, preSums.get(preSum) - 1);
+    }
+}
+