Array practice

array.js

// - slice
const p1Arr = [1, 2, 3, 4, 5, 6];
console.log(p1Arr.slice(0, 3)); // [1, 2, 3]

// - splice
const p2Arr = [1, 2, 3, 4, 5, 6];
p2Arr.splice(1, 3, 9, 9, 9);
console.log(p2Arr); // [1, 9, 9, 9, 5, 6]

// - pop
const p3Arr = [1, 2, 3, 4, 5, 6];
p3Arr.pop();
console.log(p3Arr); // [1, 2, 3, 4, 5]

// - shift
const p4Arr = [1, 2, 3, 4, 5, 6];
p4Arr.shift();
console.log(p4Arr); // [2, 3, 4, 5, 6];

// - unshift
const p5Arr = [1, 2, 3, 4, 5, 6];
p5Arr.unshift(0);
console.log(p5Arr); // [0, 1, 2, 3, 4, 5, 6];

// - every
const p6Arr = [1, 2, 3, 4, 5, 6];
console.log(p6Arr.every(p => p > 3)); // false

// - some
const p7Arr = [1, 2, 3, 4, 5, 6];
console.log(p7Arr.some(p => p > 4)); // true

// - reduce
const p8Arr = [1, 2, 3, 4, 5];
console.log(p8Arr.reduce((curr, prev) => curr + prev)); // 15

// - reduceRight
const p9Arr = [0, 1, 2, 3, 4, 5];
console.log(p9Arr.reduceRight((curr, prev) => curr + prev)); // 15

// - map
const p10Arr = [1, 2, 3, 4, 5];
console.log(p10Arr.map(p => p + 1)); // [2, 3, 4, 5, 6];

// - filter
const p11Arr = [1, 2, 3, 4, 5];
console.log(p11Arr.filter(p => p > 3)); // [4, 5];

// - forEach
const p12Arr = [1, 2, 3, 4, 5];
p12Arr.forEach((v, i) => {
  console.log(`${i}: ${v}`);
});

array_diff.js

// Notice: Only diff the same number once.

function array_diff(array1, array2) {
  var o1 = {};
  var o2 = {};
  for (var i = 0, len = array1.length; i < len; i++) {
    var val = 1;
    if (array1[i] in o1) {
      val += 1;
    }
    o1[array1[i]] = val;
  }

  for (var i = 0, len = array2.length; i < len; i++) {
    var val = 1;
    if (array2[i] in o2) {
      val += 1;
    }
    o2[array2[i]] = val;
  }

  // console.log(o1, o2);
  var result = [];

  for (var i1 in o1) {
    for (var i2 in o2) {
      if (o1[i1] === 1 && o2[i1] === 1) {
        delete o1[i1];
        delete o2[i1];
      }
    }
  }

  result = [...new Set(Object.keys(o1).concat(Object.keys(o2)))];

  return result.map(v => +v).sort(function (a, b) { return a - b; });
}

var array1 = [1, 1, 2, 2, 3, 4, 5, 7, 8, 99];
var array2 = [1, 2, 3, 4, 4, 5, 6, 8, 8, 8];

console.log(array_diff(array1, array2));  // [1, 2, 4, 6, 7, 8, 99]

sort_obj.js

var crew = [{
  age: 10
}, {
  age: 22
}, {
  age: 5
}, {
  age: 30
}];

var sortByAge = function (arr) {
  // N^2
//   for (var i = 0, maxI = arr.length; i < maxI; i++) {
//     for (var j = 0, maxJ = arr.length; j < maxJ; j++) {
//       if (+arr[i].age > +arr[j].age) {
//         var a = arr[i];
//         var b = arr[j];
//         arr[i] = b;
//         arr[j] = a;
//       }
//     }
//   }

//   return arr;

  // Quick sort (custom)
  if (arr.length <= 1) return arr;

  var pivotIndex = Math.floor(arr.length / 2) ;
  var pivot = arr.splice(pivotIndex, 1)[0];
  var left = [];
  var right = [];

  for (var i = 0; i < arr.length; i++){
    if (+arr[i].age < +pivot.age) {
      left.push(arr[i]);
    } else {
      right.push(arr[i]);
    }
  }

  return sortByAge(left).concat([pivot], sortByAge(right));

  // Sort
//   return arr.sort(function (a, b) {
//     return +a.age - +b.age;
//   });
};

console.log(sortByAge(crew));