面试题9(day2)

[robbiemie]

1.输出返回值

var length = 10; // var 定义的变量在当前作用域生效
function fn() {
  console.log(this.length);
}
var obj = {
  length: 5,
  method: function (fn) {
    fn();
    arguments[0]();
    fn.call(obj, 12); 
  },
};
obj.method(fn, 1);
function fn(e) {
  console.log(this); 
}
div.addEventListener("click", fn);

2. 实现一个带leading trailing策略的 debounce

function debounce(func, wait, options) {
  var args,
      maxTimeoutId,
      result,
      stamp,
      thisArg,
      timeoutId,
      trailingCall,
      lastCalled = 0,
      maxWait = false,
      trailing = true;

  if (typeof func != 'function') {
    throw new TypeError(FUNC_ERROR_TEXT);
  }
  wait = wait < 0 ? 0 : (+wait || 0);
  if (options === true) {
    var leading = true;
    trailing = false;
  } else if (isObject(options)) {
    leading = !!options.leading;
    maxWait = 'maxWait' in options && nativeMax(+options.maxWait || 0, wait);
    trailing = 'trailing' in options ? !!options.trailing : trailing;
  }

  function complete(isCalled, id) {
    if (id) {
      clearTimeout(id);
    }
    maxTimeoutId = timeoutId = trailingCall = undefined;
    if (isCalled) {
      lastCalled = now();
      result = func.apply(thisArg, args);
      if (!timeoutId && !maxTimeoutId) {
        args = thisArg = undefined;
      }
    }
  }

  function delayed() {
    var remaining = wait - (now() - stamp);
    if (remaining <= 0 || remaining > wait) {
      complete(trailingCall, maxTimeoutId);
    } else {
      timeoutId = setTimeout(delayed, remaining);
    }
  }

  function maxDelayed() {
    complete(trailing, timeoutId);
  }

  function debounced() {
    args = arguments;
    stamp = now();
    thisArg = this;
    trailingCall = trailing && (timeoutId || !leading);

    if (maxWait === false) {
      var leadingCall = leading && !timeoutId;
    } else {
      if (!maxTimeoutId && !leading) {
        lastCalled = stamp;
      }
      var remaining = maxWait - (stamp - lastCalled),
          isCalled = remaining <= 0 || remaining > maxWait;

      if (isCalled) {
        if (maxTimeoutId) {
          maxTimeoutId = clearTimeout(maxTimeoutId);
        }
        lastCalled = stamp;
        result = func.apply(thisArg, args);
      }
      else if (!maxTimeoutId) {
        maxTimeoutId = setTimeout(maxDelayed, remaining);
      }
    }
    if (isCalled && timeoutId) {
      timeoutId = clearTimeout(timeoutId);
    }
    else if (!timeoutId && wait !== maxWait) {
      timeoutId = setTimeout(delayed, wait);
    }
    if (leadingCall) {
      isCalled = true;
      result = func.apply(thisArg, args);
    }
    if (isCalled && !timeoutId && !maxTimeoutId) {
      args = thisArg = undefined;
    }
    return result;
  }
  return debounced;
}

3. 假设你正在爬楼梯。需要 n 阶你才能到达楼顶。 每次你可以爬 1 或 2 个台阶。你有多少种不同的方法可以爬到楼顶呢？

// 递归法
function climbStairs(n: number): number {
    if(n === 0) return 0;
    if(n === 1) return 1;
    if(n === 2) return 2;

    return climbStairs(n-1) + climbStairs(n-2);
};
// dp
function climbStairs(n) {
  let arr = []
  arr[0] = 0;
  arr[1] = 1;
  arr[2] = 2;

  for(let i=3;i<=n;i++) {
    arr[i] = arr[i-1] + arr[i-2]
  }

  return arr[n]
}