# Maximum subarray

JavaScript, Algorithm, Math, Array · Sep 7, 2022

Finds a contiguous subarray with the largest sum within an array of numbers.

• Use a greedy approach to keep track of the current `sum` and the current maximum, `maxSum`. Set `maxSum` to `-Infinity` to make sure that the highest negative value is returned, if all values are negative.
• Define variables to keep track of the maximum start index, `sMax`, maximum end index, `eMax` and current start index, `s`.
• Use `Array.prototype.forEach()` to iterate over the values and add the current value to the `sum`.
• If the current `sum` is greater than `maxSum`, update the index values and the `maxSum`.
• If the `sum` is below `0`, reset it to `0` and update the value of `s` to the next index.
• Use `Array.prototype.slice()` to return the subarray indicated by the index variables.
```const maxSubarray = (...arr) => {
let maxSum = -Infinity,
sum = 0;
let sMax = 0,
eMax = arr.length - 1,
s = 0;

arr.forEach((n, i) => {
sum += n;
if (maxSum < sum) {
maxSum = sum;
sMax = s;
eMax = i;
}

if (sum < 0) {
sum = 0;
s = i + 1;
}
});

return arr.slice(sMax, eMax + 1);
};```
`maxSubarray(-2, 1, -3, 4, -1, 2, 1, -5, 4); // [4, -1, 2, 1]`

### Written by Angelos Chalaris

I'm Angelos Chalaris, a JavaScript software engineer, based in Athens, Greece. The best snippets from my coding adventures are published here to help others learn to code.

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