Add Path Sum TS Solution

Author: JeremyXXXuuu

Problems/04-Path-Sum/Path-Sum.ts

@@ -0,0 +1,52 @@
+ /**
+ * Definition for a binary tree node.
+ * class TreeNode {
+ *     val: number
+ *     left: TreeNode | null
+ *     right: TreeNode | null
+ *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
+ *         this.val = (val===undefined ? 0 : val)
+ *         this.left = (left===undefined ? null : left)
+ *         this.right = (right===undefined ? null : right)
+ *     }
+ * }
+ */
+
+ /**
+ * Definition for a binary tree node.
+ * class TreeNode {
+ *     val: number
+ *     left: TreeNode | null
+ *     right: TreeNode | null
+ *     constructor(val?: number, left?: TreeNode | null, right?: TreeNode | null) {
+ *         this.val = (val===undefined ? 0 : val)
+ *         this.left = (left===undefined ? null : left)
+ *         this.right = (right===undefined ? null : right)
+ *     }
+ * }
+ */
+
+ function hasPathSum(root: TreeNode | null, targetSum: number): boolean {
+    if(!root) return false;
+    let res: boolean = false;
+    let sum: number = 0;
+    //不是简洁的写法，但是回溯思路比较清晰
+    function dfs(node: TreeNode | null) {
+        if(!node) return;
+        if(node.left === null && node.right === null){
+            if(sum + node.val === targetSum){
+                res = true;
+                return
+            }
+        }
+        sum += node.val;
+        dfs(node.left);
+        sum -= node.val;
+        
+        sum += node.val;
+        dfs(node.right);
+        sum -= node.val;
+    }
+    dfs(root);
+    return res;
+}