算法与数据结构学习

Chapter4/stack.mjs

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+function push(element) {
+  this.dataSource[this.top++] = element;
+}
+
+function pop() {
+  return this.dataSource[--this.top];
+}
+
+function peek() {
+  return this.dataSource[this.top - 1];
+}
+
+function length() {
+  return this.top;
+}
+
+function clear() {
+  this.top = 0;
+}
+
+export default function Stack() {6
+  this.dataSource = [];
+  this.top = 0;
+  this.push = push;
+  this.pop = pop;
+  this.peek = peek;
+  this.length = length;
+  this.clear = clear;
+}

Chapter4/test1.mjs

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+import Stack from "./stack.mjs";
+// 找出缺失的括号
+function findMissingParentheses(expression) {
+  const stack = new Stack();
+  const expressionList = expression.split('');
+  for (let i = 0; i < expressionList.length; i++) { 
+    const char = expressionList[i];
+    if (char === '(') {
+      stack.push(i);
+    }
+    if (char === ')') {
+      stack.pop();
+    }
+  }
+  if (stack.length() > 0) {
+    console.log('missing parent index:', stack.pop());
+  }
+}
+
+findMissingParentheses('2.3 + 23 / 12 + (3.14159 x 0.24')

Chapter4/test2.mjs

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+import Stack from "./stack.mjs";
+
+function infixToPostfix(infixExpression) {
+  const stack1 = new Stack();
+  const stack2 = new Stack();
+
+  function warOperator(operator1, operator2) {
+    if (operator2 === undefined || operator2 === "(") {
+      stack1.push(operator1);
+    } else {
+      if (["x", "/"].includes(operator1) && ["+", "-"].includes(operator2)) {
+        stack1.push(operator1);
+      } else {
+        const top = stack1.pop();
+        stack2.push(top);
+        const nextOperator = stack1.peek();
+        warOperator(operator1, nextOperator);
+      }
+    }
+  }
+
+  const dealInfixExpression = infixExpression.replaceAll(" ", "");
+
+  let numStr = "";
+  for (let i = 0; i < dealInfixExpression.length; i++) {
+    const char = dealInfixExpression[i];
+    if (["+", "-", "x", "/"].includes(char)) {
+      if (numStr.length > 0) {
+        stack2.push(numStr);
+        numStr = "";
+      }
+      const topOperator = stack1.peek();
+      warOperator(char, topOperator);
+    } else if (["(", ")"].includes(char)) {
+      if (numStr.length > 0) {
+        stack2.push(numStr);
+        numStr = "";
+      }
+      if (char === "(") {
+        stack1.push(char);
+      } else {
+        while (stack1.length()) {
+          let operator = stack1.pop();
+          if (operator === "(") {
+            break;
+          }
+          stack2.push(operator);
+        }
+      }
+    } else {
+      numStr += char;
+      if (i === dealInfixExpression.length - 1) {
+        stack2.push(numStr);
+      }
+    }
+  }
+
+  while (stack1.length()) {
+    stack2.push(stack1.pop());
+  }
+
+  const postfixExpression = [];
+  while (stack2.length()) {
+    postfixExpression.push(stack2.pop());
+  }
+  postfixExpression.reverse();
+  return postfixExpression;
+}
+
+function calc(num1, num2, operator) {
+  const n1 = Number(num1);
+  const n2 = Number(num2);
+  let result;
+  switch (operator) {
+    case "+":
+      result = n1 + n2;
+      break;
+    case "-":
+      result = n1 - n2;
+      break;
+    case "x":
+      result = n1 * n2;
+      break;
+    case "/":
+      result = n1 / n2;
+      break;
+  }
+  return result;
+}
+
+function calculate(postfixExpression) {
+  const stack = new Stack();
+  for (let i = 0; i < postfixExpression.length; i++) {
+    const element = postfixExpression[i];
+    if (["+", "-", "x", "/"].includes(element)) {
+      const num2 = stack.pop();
+      const num1 = stack.pop();
+      stack.push(calc(num1, num2, element));
+    } else {
+      stack.push(element);
+    }
+  }
+
+  return stack.pop();
+}
+
+const expression = "12+((2.1+3) x45.2)-5.22";
+const postfixExpression = infixToPostfix(expression);
+console.log(postfixExpression);
+const result = calculate(postfixExpression);
+console.log(result);