Locate the indices of several maximum values within an array

Question

Locate the indices of several maximum values within an array

Here is an array for reference:

var exampleArray = [10, 67, 100, 100];

The goal is to identify the indexes of the maximum values in the array.

The existing function currently locates only one index:

function findMaxIndexes(arr) {
      var max = arr[0];
      var maxIndexes = [0];
      for (var i = 1; i < arr.length; i++) {
          if (arr[i] > max) {
              maxIndexes = [i];
              max = arr[i];
          } else if (arr[i] === max) {
              maxIndexes.push(i);
          }
      }
      return maxIndexes;
 }

To update the function to return an array of max indexes, modify it as follows:

When used with the example array provided earlier, the modified function should return:

[2, 3].

javascript arrays

Answer 1

Answer №1

To efficiently keep track of multiple indices instead of just one, consider implementing the following code snippet:

function findMaxIndices(arr) {
    var max = -Infinity;
    var maxIndices = [];
    for (var i = 0; i < arr.length; i++) {
        if (arr[i] === max) {
          maxIndices.push(i);
        } else if (arr[i] > max) {
            maxIndices = [i];
            max = arr[i];
        }
    }
    return maxIndices;
 }

Answer 2

To efficiently keep track of multiple indices instead of just one, consider implementing the following code snippet:

function findMaxIndices(arr) {
    var max = -Infinity;
    var maxIndices = [];
    for (var i = 0; i < arr.length; i++) {
        if (arr[i] === max) {
          maxIndices.push(i);
        } else if (arr[i] > max) {
            maxIndices = [i];
            max = arr[i];
        }
    }
    return maxIndices;
 }

Answer 3

Answer №2

This is my approach:

let numbers = [5, 34, 76, 98],
      max = Math.max(...numbers),
  indexMax = numbers.reduce((prev, curr, i, arr) => curr == max ? prev.concat(i) : prev,[]);
console.log(indexMax);

Answer 4

This is my approach:

let numbers = [5, 34, 76, 98],
      max = Math.max(...numbers),
  indexMax = numbers.reduce((prev, curr, i, arr) => curr == max ? prev.concat(i) : prev,[]);
console.log(indexMax);

Answer 5

Answer №3

const findIndexOfMaxValue = (arr) => {
    const maxVal = Math.max(...arr);
    
    const indexes = [];
    arr.forEach((num, index) => {
        if (num === maxVal) {
            indexes.push(index);
        }
    });
    
    return indexes;
}

const numbers = [5, 10, 15, 10];
console.log(findIndexOfMaxValue(numbers));

Answer 6

const findIndexOfMaxValue = (arr) => {
    const maxVal = Math.max(...arr);
    
    const indexes = [];
    arr.forEach((num, index) => {
        if (num === maxVal) {
            indexes.push(index);
        }
    });
    
    return indexes;
}

const numbers = [5, 10, 15, 10];
console.log(findIndexOfMaxValue(numbers));

Answer 7

Answer №4

After reviewing this comparison of runtimes, I suggest implementing an optimized for-loop to search for the max indices:

function max(arr) {
  var max = -Infinity, indices = [];
  for (var i = 0; i < arr.length; ++i) {
    if (arr[i] < max) continue;
    if (arr[i] > max) {
      indices = [];
      max = arr[i];
    }
    indices.push(i);
  }
  return indices;
}

console.log(max([10, 67, 100, 100])); // [2, 3]

Starting with the comparison arr[i] < max is beneficial as it is true most of the time, allowing us to move to the next iteration with only one array access and comparison on average.

Runtime comparison of the different suggested algorithms:

Based on https://jsfiddle.net/jv1z29jm/2/ - feel free to make updates.

Chrome (48):

max_indexOf x 15,381 ops/sec ±2.94% (87 runs sampled)
max_reduce x 2,909 ops/sec ±2.63%(86 runs sampled)
max_forloop x 119,964 ops/sec ±1.80% (87 runs sampled)
max_forloopOptimized x 165,581 ops/sec ±1.50% (87 runs sampled)
Fastest is max_forloopOptimized

Firefox (46):

max_indexOf x 56,456 ops/sec ±0.74% (67 runs sampled)
max_reduce x 74,959 ops/sec ±0.86% (65 runs sampled)
max_forloop x 73,223 ops/sec ±24.75% (58 runs sampled)
max_forloopOptimized x 84,567 ops/sec ±9.99% (61 runs sampled)
Fastest is max_forloopOptimized

Answer 8

After reviewing this comparison of runtimes, I suggest implementing an optimized for-loop to search for the max indices:

function max(arr) {
  var max = -Infinity, indices = [];
  for (var i = 0; i < arr.length; ++i) {
    if (arr[i] < max) continue;
    if (arr[i] > max) {
      indices = [];
      max = arr[i];
    }
    indices.push(i);
  }
  return indices;
}

console.log(max([10, 67, 100, 100])); // [2, 3]

Starting with the comparison arr[i] < max is beneficial as it is true most of the time, allowing us to move to the next iteration with only one array access and comparison on average.

Runtime comparison of the different suggested algorithms:

Based on https://jsfiddle.net/jv1z29jm/2/ - feel free to make updates.

Chrome (48):

max_indexOf x 15,381 ops/sec ±2.94% (87 runs sampled)
max_reduce x 2,909 ops/sec ±2.63%(86 runs sampled)
max_forloop x 119,964 ops/sec ±1.80% (87 runs sampled)
max_forloopOptimized x 165,581 ops/sec ±1.50% (87 runs sampled)
Fastest is max_forloopOptimized

Firefox (46):

max_indexOf x 56,456 ops/sec ±0.74% (67 runs sampled)
max_reduce x 74,959 ops/sec ±0.86% (65 runs sampled)
max_forloop x 73,223 ops/sec ±24.75% (58 runs sampled)
max_forloopOptimized x 84,567 ops/sec ±9.99% (61 runs sampled)
Fastest is max_forloopOptimized

Answer 9

Answer №5

Utilizing JS's Reduce method can be beneficial for solving this particular task.

// Function to find the maximum value in an array
var maxArrSingle = function(arr) {
  return arr.reduce(
    function(acc,val){
      return Math.max(acc,val);
    },
    -Infinity);
}

// Function to find indices where array values are at the maximum
var maxArrIndexes = function(arr) {
  var max = maxArrSingle(arr);
  return arr.reduce(function(acc,val,idx) {
    if (val >= max) acc.push(idx);
    return acc;
  },[]);
}

// Demos
var arr = [10, 67, 100, 100];
console.log(maxArrIndexes(arr));

var arr = [-10, -67, -100, -100, -4000, -9, -90, -90 ];
console.log(maxArrIndexes(arr));

var arr = [];
console.log(maxArrIndexes(arr));

var arr = [0];
console.log(maxArrIndexes(arr));

var arr = [0,0];
console.log(maxArrIndexes(arr));

Answer 10

Utilizing JS's Reduce method can be beneficial for solving this particular task.

// Function to find the maximum value in an array
var maxArrSingle = function(arr) {
  return arr.reduce(
    function(acc,val){
      return Math.max(acc,val);
    },
    -Infinity);
}

// Function to find indices where array values are at the maximum
var maxArrIndexes = function(arr) {
  var max = maxArrSingle(arr);
  return arr.reduce(function(acc,val,idx) {
    if (val >= max) acc.push(idx);
    return acc;
  },[]);
}

// Demos
var arr = [10, 67, 100, 100];
console.log(maxArrIndexes(arr));

var arr = [-10, -67, -100, -100, -4000, -9, -90, -90 ];
console.log(maxArrIndexes(arr));

var arr = [];
console.log(maxArrIndexes(arr));

var arr = [0];
console.log(maxArrIndexes(arr));

var arr = [0,0];
console.log(maxArrIndexes(arr));

Answer 11

Answer №6

Here is a simple solution for finding the maximum value in an array and then returning the indexes of all occurrences of that max value.

function findMaxIndexes(arr){

var maxValue = Math.max(...arr);
var maxIndexes = [];

for(let i = 0; i < arr.length; i++){
if(arr[i] === maxValue){
maxIndexes.push(i);
}
}
return maxIndexes;
};

var numbers = [8, 45, 94, 94];
console.log(findMaxIndexes(numbers));

Answer 12

Here is a simple solution for finding the maximum value in an array and then returning the indexes of all occurrences of that max value.

function findMaxIndexes(arr){

var maxValue = Math.max(...arr);
var maxIndexes = [];

for(let i = 0; i < arr.length; i++){
if(arr[i] === maxValue){
maxIndexes.push(i);
}
}
return maxIndexes;
};

var numbers = [8, 45, 94, 94];
console.log(findMaxIndexes(numbers));

Locate the indices of several maximum values within an array

Answer №1

Answer №2

Answer №3

Answer №4

Answer №5

Answer №6

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