javascript - 返回最大的数组

Question

我一直在尝试解决这个练习题:

Return an array consisting of the largest number from each provided sub-array. For simplicity, the provided array will contain exactly 4 sub-arrays.

但我的代码只返回整个数组中的单个元素，如果我unshift 所有最大元素它会产生完全错误的结果，我尝试单独执行嵌套循环并且它工作正常但与外循环结合使用时会产生问题。

function largestOfFour(arr)
{
    // You can do this!
    var max = 0;
    var largestArray =[];
    for (var i = 0; i <4; i++)
    {
        for (var j = 0; j <4; j++)
        {
            if (arr[i][j]>max)
            {
              max=arr[i][j];
              largestArray.unshift(max);
              //console.log(max);
            }

        }
    }
      console.log(largestArray);
    return max;
}

largestOfFour([[4, 5, 1, 13], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]);

Answer 1

如何修复您的代码(参见代码中的注释):

function largestOf(arr) {
  var max;
  var largestArray = [];

  for (var i = 0; i < arr.length; i++) { // the arr length is the number of sub arrays
    max = -Infinity; // max should be reinitialized to the lowest number on each loop
    for (var j = 0; j < arr[i].length; j++) { // the length is the number of items in the sub array
      if (arr[i][j] > max) { // just update max to a higher number
        max = arr[i][j];
      }
    }
    
    largestArray.push(max); // push max after the internal loop is done, and max is known
  }

  return largestArray; // return the largest array
}

var result = largestOf([[4, 5, 1, 13], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]);

console.log(result);

另一个解决方案是使用 Array#map , 并申请 Math#max到每个子数组以获得它的最大值:

function largestOf(arr) {
  return arr.map(function(s) {
    return Math.max.apply(Math, s);
  });
}

var result = largestOf([[4, 5, 1, 13], [13, 27, 18, 26], [32, 35, 37, 39], [1000, 1001, 857, 1]]);

console.log(result);