Create 150. 逆波兰表达式求值.js

Author: yinxin630

150. 逆波兰表达式求值.js

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+/**
+ * @param {string[]} tokens
+ * @return {number}
+ */
+var evalRPN = function(tokens) {
+  function isOperator(char) {
+    return ['+', '-', '*', '/'].includes(char);
+  }
+  function getResult(n1, n2, opr) {
+    switch (opr) {
+      case '+': {
+        return n2 + n1;
+        break;
+      }
+      case '-': {
+        return n2 - n1;
+        break;
+      }
+      case '*': {
+        return n2 * n1;
+        break;
+      }
+      case '/': {
+        return (n2 / n1) > 0 ? Math.floor(n2 / n1) : Math.ceil(n2 / n1);
+        break;
+      }
+    }
+  }
+
+  const stack = [];
+  for (let i = 0; i < tokens.length ; i++) {
+    if (isOperator(tokens[i])) {
+      stack.push(getResult(stack.pop(), stack.pop(), tokens[i]))
+    } else {
+      stack.push(parseInt(tokens[i]));
+    }
+  }
+  return stack[0];
+};