Update 1597-build-binary-expression-tree-from-infix-expression.js

Author: everthis

1597-build-binary-expression-tree-from-infix-expression.js

@@ -1,3 +1,62 @@
+/**
+ * Definition for a binary tree node.
+ * function Node(val, left, right) {
+ *     this.val = (val===undefined ? " " : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {string} s
+ * @return {Node}
+ */
+const expTree = function (s) {
+  const n = s.length
+  const head = new Node()
+  let i = 0
+  const number = () => {
+    let num = ''
+    while (i < n && '0' <= s[i] && s[i] <= s[i]) {
+      num += s[i++]
+    }
+    return new Node(Number(num))
+  }
+  const factor = () => {
+    if (s[i] === '(') {
+      i++
+      const node = expression()
+      i++
+      return node
+    }
+    return number()
+  }
+  const term = () => {
+    let left = factor()
+    while (i < n && (s[i] === '*' || s[i] === '/')) {
+      const op = new Node(s[i++])
+      const right = factor()
+      op.left = left
+      op.right = right
+      left = op
+    }
+    return left
+  }
+  const expression = () => {
+    let left = term()
+    while (i < s.length && (s[i] === '+' || s[i] === '-')) {
+      const op = new Node(s[i++])
+      const right = term()
+      op.left = left
+      op.right = right
+      left = op
+    }
+    return left
+  }
+  return expression()
+}
+
+// another
+
 /**
  * Definition for a binary tree node.
  * function Node(val, left, right) {