The question
Given an array of integers (positive and negative) find the largest continuous sum.
My solution
These are the steps I followed:
– Get the first number and add it to a variable where you will store the largest sum so far(largest).
– Create another variable(currentSum) where you will store the value of the current sum so far and assign the same number to it.
– Move to the next number. Calculate the sum of n1 and n2, if it is positive then assign it to currentSum.
– Check if currentSum is larger that largest. If it is, update largest.
– If currentSum became negative then assign 0 to it.
You have to go through each number in the array once, so the complexity is O(N).
The implementation
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function findLargestSum(arr) {
// Start both variables with the value of the first element
var largest = arr[0];
var current = arr[0];
for (var i = 1; i < arr.length; i++) {
var sum = current + arr[i];
// If sum becomes negative restart it to 0
if (sum < 0) {
current = 0;
} else {
current = sum;
}
// If sum becomes greater than largest then
// update largest
if (sum > largest) {
largest = sum;
}
}
return largest;
}
function test() {
var input = [1, 2, 3, -1, 7, -12, -3, 45, -27, -1, 4, 30, -100, 1];
// The largest sum for this array is 51
if (51 === findLargestSum(input)) {
console.log('success');
} else {
console.log('failure');
}
}
test();
A friend suggested to make this exercise a little more complicated by also printing the sequence that gives that result. Here is the code for that:
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function findLargestSum(arr) {
var largest = arr[0];
var current = arr[0];
var currentStart = 0;
var currentEnd = 0;
var largestStart = 0;
var largestEnd = 0;
for (var i = 1; i < arr.length; i++) {
var sum = current + arr[i];
if (sum < 0) {
current = 0;
currentStart = i + 1;
} else {
current = sum;
}
if (sum > largest) {
largestStart = currentStart;
largestEnd = currentEnd = i;
largest = sum;
}
}
var resultArray = [];
for (i = largestStart; i <= largestEnd; i++) {
resultArray.push(arr[i]);
}
return resultArray;
}
function test() {
var input = [1, 2, 3, -1, 7, -12, -3, 45, -27, -1, 4, 30, -100, 1];
var expected = [45, -27, -1, 4, 30];
if (expected.toString() === findLargestSum(input).toString()) {
console.log('success');
} else {
console.log('failure');
}
}
test();
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