数据结构基础

FreeCodeCamp
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数据结构基础主要讲了数组和对象的特性和基本方法。

  • 数组

    • 获取数组元素的方法array[index]
    • 添加删除元素
      • array.push(ele) 数组末尾添加ele
      • array.shift(ele) 数组开头添加ele
      • array.pop() 删除数组末尾元素
      • array.unshift() 删除数组开头元素
      • array.splice(index, len) 删除数组从位于index开始的的元素，删除长度为len
      • array.splice(index, len, ele) 删除数组从位于index开始的元素，删除长度为len,并添加ele
    • 扩展运算符[...arr]
      • 利用扩展运算符赋值数组
      • 利用扩展运算符合并数组
    • 检测数组是否包含某个元素array.indexOf(ele)，如果包含，则返回ele所在的index，如果不包含，返回-1
    • 利用for循环遍历数组for(let i = 0; i < len; i ++)
    • 多维数组

  • Object

    • 多维Object
    • 获取对象的值
      • obj.key
      • obj["key"]
    • 删除对象的值 delete obj.key
    • 检测对象是否包含某个属性 obj.hasOwnProperty(key)
    • 利用for…in循环遍历对象for(let i in obj)
    • 获取对象的所有属性 Object.keys(obj)，返回一个全是对象属性的数组

这一部分内容比较基础，难度不大。以下是这部分的习题解答：

Introduction to the Basic Data Structure Challenges

  • Use an Array to Store a Collection of Data

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    let yourArray = [true, "abc", 12, [1, 2], {a: 1, b: 2}]; // change this line

  • Access an Array’s Contents Using Bracket Notation

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    let myArray = ["a", "b", "c", "d"];
    // change code below this line
    myArray[1] = "hello";
    //change code above this line
    console.log(myArray);

  • Add Items to an Array with push() and unshift()

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    function mixedNumbers(arr) {
      // change code below this line
        arr.unshift('I', 2, 'three');
        arr.push(7, 'VIII', 9);
      // change code above this line
      return arr;
    }

    // do not change code below this line
    console.log(mixedNumbers(['IV', 5, 'six']));

  • Remove Items from an Array with pop() and shift()

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    function popShift(arr) {
      let popped = arr.pop(); // change this line
      let shifted = arr.shift(); // change this line
      return [shifted, popped];
    }

    // do not change code below this line
    console.log(popShift(['challenge', 'is', 'not', 'complete']));

  • Remove Items Using splice()

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    function sumOfTen(arr) {
      // change code below this line
      arr.splice(1,2);
      // change code above this line
      return arr.reduce((a, b) => a + b);
    }

    // do not change code below this line
    console.log(sumOfTen([2, 5, 1, 5, 2, 1]));

  • Add Items Using splice()

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    function htmlColorNames(arr) {
      // change code below this line
      arr.splice(0, 2, "DarkSalmon", "BlanchedAlmond");
      // change code above this line
      return arr;
    } 
     
    // do not change code below this line
    console.log(htmlColorNames(['DarkGoldenRod', 'WhiteSmoke', 'LavenderBlush', 'PaleTurqoise', 'FireBrick']));

  • Copy Array Items Using slice()

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    function forecast(arr) {
      // change code below this line
      return arr.slice(2, 4);
    }

    // do not change code below this line
    console.log(forecast(['cold', 'rainy', 'warm', 'sunny', 'cool', 'thunderstorms']));

  • Copy an Array with the Spread Operator

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    function copyMachine(arr, num) {
      let newArr = [];
      while (num >= 1) {
        // change code below this line
        newArr.push([...arr]);
        // change code above this line
        num--;
      }
      return newArr;
    }

    // change code here to test different cases:
    console.log(copyMachine([true, false, true], 2));

  • Combine Arrays with the Spread Operator

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    function spreadOut() {
      let fragment = ['to', 'code'];
      let sentence = ['learning', ...fragment, 'is', 'fun']; // change this line
      return sentence;
    }

    // do not change code below this line
    console.log(spreadOut());

  • Check For The Presence of an Element With indexOf()

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    function quickCheck(arr, elem) {
      // change code below this line
      if(arr.indexOf(elem) === -1) {
        return false;
      }
      return true;
      // change code above this line
    }

    // change code here to test different cases:
    console.log(quickCheck(['squash', 'onions', 'shallots'], 'mushrooms'));

  • Iterate Through All an Array’s Items Using For Loops

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    function filteredArray(arr, elem) {
      let newArr = [];
      // change code below this line
      for(let i = 0; i < arr.length; i ++) {
        if(arr[i].indexOf(elem) === -1){
          newArr.push(arr[i]);
        }
      }
      // change code above this line
      return newArr;
    }

    // change code here to test different cases:
    console.log(filteredArray([[3, 2, 3], [1, 6, 3], [3, 13, 26], [19, 3, 9]], 3));

  • Create complex multi-dimensional arrays

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    let myNestedArray = [
      // change code below this line
      ['unshift', false, 1, 2, 3, 'complex', 'nested',['deep', ['deeper', ['deepest']]]],
      ['loop', 'shift', 6, 7, 1000, 'method'],
      ['concat', false, true, 'spread', 'array'],
      ['mutate', 1327.98, 'splice', 'slice', 'push'],
      ['iterate', 1.3849, 7, '8.4876', 'arbitrary', 'depth']
      // change code above this line
    ];

  • Add Key-Value Pairs to JavaScript Objects

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    let foods = {
      apples: 25,
      oranges: 32,
      plums: 28
    };

    // change code below this line
    foods.bananas = 13;
    foods.grapes = 35;
    foods["strawberries"] = 27;
    // change code above this line

    console.log(foods);

  • Modify an Object Nested Within an Object

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    let userActivity = {
      id: 23894201352,
      date: 'January 1, 2017',
      data: {
        totalUsers: 51,
        online: 42
      }
    };

    // change code below this line
    userActivity.data.online = 45;
    // change code above this line

    console.log(userActivity);

  • Access Property Names with Bracket Notation

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    let foods = {
      apples: 25,
      oranges: 32,
      plums: 28,
      bananas: 13,
      grapes: 35,
      strawberries: 27
    };
    // do not change code above this line

    function checkInventory(scannedItem) {
      // change code below this line
      return foods[scannedItem];
    }

    // change code below this line to test different cases:
    console.log(checkInventory("apples"));

  • Use the delete Keyword to Remove Object Properties

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    let foods = {
      apples: 25,
      oranges: 32,
      plums: 28,
      bananas: 13,
      grapes: 35,
      strawberries: 27
    };

    // change code below this line
    delete foods.oranges;
    delete foods.plums;
    delete foods.strawberries;
    // change code above this line

    console.log(foods);

  • Check if an Object has a Property

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    let users = {
      Alan: {
        age: 27,
        online: true
      },
      Jeff: {
        age: 32,
        online: true
      },
      Sarah: {
        age: 48,
        online: true
      },
      Ryan: {
        age: 19,
        online: true
      }
    };

    function isEveryoneHere(obj) {
      // change code below this line
      if(obj.hasOwnProperty('Alan') && obj.hasOwnProperty('Jeff') && obj.hasOwnProperty('Sarah') && obj.hasOwnProperty('Ryan')) {
        return true;
      }
      return false;
      // change code above this line
    }

    console.log(isEveryoneHere(users));

  • Iterate Through the Keys of an Object with a for…in Statement

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    let users = {
      Alan: {
        age: 27,
        online: false
      },
      Jeff: {
        age: 32,
        online: true
      },
      Sarah: {
        age: 48,
        online: false
      },
      Ryan: {
        age: 19,
        online: true
      }
    };

    function countOnline(obj) {
      // change code below this line
      let result = 0;
      for(let i in obj) {
        if(obj[i].online === true) {
          result =result +=1;
        }
      }
      return result;
      // change code above this line
    }

    console.log(countOnline(users));

  • Generate an Array of All Object Keys with Object.keys()

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    let users = {
      Alan: {
        age: 27,
        online: false
      },
      Jeff: {
        age: 32,
        online: true
      },
      Sarah: {
        age: 48,
        online: false
      },
      Ryan: {
        age: 19,
        online: true
      }
    };

    function getArrayOfUsers(obj) {
      // change code below this line
      return Object.keys(obj);
      // change code above this line
    }

    console.log(getArrayOfUsers(users));

  • Modify an Array Stored in an Object

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    let user = {
      name: 'Kenneth',
      age: 28,
      data: {
        username: 'kennethCodesAllDay',
        joinDate: 'March 26, 2016',
        organization: 'freeCodeCamp',
        friends: [
          'Sam',
          'Kira',
          'Tomo'
        ],
        location: {
          city: 'San Francisco',
          state: 'CA',
          country: 'USA'
        }
      }
    };

    function addFriend(userObj, friend) {
      // change code below this line  
      userObj.data.friends.push(friend);
      return userObj.data.friends;
      // change code above this line
    }

    console.log(addFriend(user, 'Pete'));