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

Author: everthis

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

@@ -0,0 +1,48 @@
+/**
+ * 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 list = s.split('')
+  const mdSet = new Set(['*', '/'])
+  const amSet = new Set(['+', '-'])
+  return parseExpression(list)
+  
+  function parseExpression(tokens) {
+    let lhs = parseTerm(tokens)
+    while(tokens.length && amSet.has(tokens[0])) {
+      const op = tokens.shift()
+      const rhs = parseTerm(tokens)
+      lhs = new Node(op, lhs, rhs)
+    }
+    return lhs
+  }
+  function parseTerm(tokens) {
+    let lhs = parseFactor(tokens)
+    while(tokens.length && mdSet.has(tokens[0])) {
+      const op = tokens.shift()
+      const rhs = parseFactor(tokens)
+      lhs = new Node(op, lhs, rhs)
+    }
+    return lhs
+  }
+  function parseFactor(tokens) {
+    if(tokens[0] === '(') {
+      tokens.shift()
+      const node = parseExpression(tokens)
+      tokens.shift()
+      return node
+    } else {
+      const token = tokens.shift()
+      return new Node(token)
+    } 
+  }
+};