JavaScript常見演算法集合

wdapp發表於2020-02-04
JavaScript演算法

氣泡排序法

var arrays = [81, 23, 46, 11, 56, 69, 57, 78, 99, 21, 23];
for (var i = 0; i < arrays.length - 1; i++) {
  for (var j = 0; j < arrays.length - 1 - i; j++) {
    if (arrays[j] > arrays[j + 1]) {
      var t = arrays[j + 1];
      arrays[j + 1] = arrays[j];
      arrays[j] = t;
    }
  }
}
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選擇排序法

var arrays = [81, 23, 46, 11, 56, 69, 57, 78, 99, 21, 23];
//選擇排序法
for (var i = 0; i < arrays.length - 1; i++) {
  for (var j = i + 1; j < arrays.length; j++) {
    if (arrays[i] > arrays[j]) {
      var t = arrays[i];
      arrays[i] = arrays[j];
      arrays[j] = t;
    }
  }
}
console.log(arrays);
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函式柯里化

// 函式柯里化：利用返回函式的方式，將多個引數進行分解，單一引數。

// 普通函式
function add(x, y) {
  return x + y;
}

// 函式柯里化
function add(x) {
  return function(y) {
    return x + y;
  };
}

console.log(add(1)(2))
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// 函式柯里化封裝
function add(x, y) {
  return x + y;
}

function curried(fn, ...arg1) {
  return function(...arg2) {
    return fn(...arg1, ...arg2);
  };
}

var increment = curried(add, 1);
console.log(increment(2));

// 函式柯里化更適合函數語言程式設計方法

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new 實現原理

function myFun() {

}

var f = new myFun();

console.log(f instanceof myFun);
console.log(_instanceof(f, myFun));
var s = "str"
console.log(_instanceof(s, String));
console.log(s instanceof String);

function _instanceof(left, right) {
  var left = left.__proto__;
  var prototype = right.prototype;
  while (true) {
    if (left == null) {
      return false;
    }
    if (left == prototype) {
      return true;
    }
    left = left.__proto__;
  }
}
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陣列去重

var arr = [2,5,3,6,2,4,5,8,3]
var obj = {}
for (var i = 0; i < arr.length; i++) {
    if(!obj[arr[i]]){
      obj[arr[i]] = 1
    }
}
console.log(obj)
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斐波那契數列

function fibonacci(n) {
  return n < 2 ? n : fibonacci(n - 1) + fibonacci(n - 2);
}
console.log(fibonacci(5)) // 1 1 2 3 5
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JavaScript深拷貝

var obj1 = {
  o: {
    name: "hello"
  },
  arr: [1, 2, {
    pass: 333
  }],
  str: "world"
};

function isType(target) {
  return Object.prototype.toString.call(target).slice(8, -1);
}

function deepCopy(target) {
  var type = isType(target);
  var reslut;
  if (type === "Array") {
    reslut = [];
  } else if (type === "Object") {
    reslut = {};
  } else {
    return target
  }
  for (var key in target) {
    var value = target[key];
    if (isType(value) === "Object" || isType(value) === "Array") {
      reslut[key] = deepCopy(value);
    } else {
      reslut[key] = value;
    }
  }
  return reslut;
}

var obj2 = deepCopy(obj1);

obj2.o.name = "hello x";
obj2.arr[0] = 11;
obj2.arr.push(4);
obj2.arr[2].pass = 555;
obj2.str = "world x";

console.log("new obj1", obj1);
console.log("new obj2", obj2);
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統計出現組多的元素

var arr = ["1", "2", "345", "3", "21", "345","4", "23", "88", "25", "2", "3", "99"];
var maxStack = {};
for (var i = 0; i < arr.length; i++) {
  var item = arr[i];
  if (!maxStack[item]) {
    maxStack[item] = 1;
  } else {
    maxStack[item] = maxStack[item] + 1;
  }
}
console.log(maxStack);
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