Add maxSubarray

snippets/maxSubarray.md

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+---
+title: Maximum subarray
+tags: algorithm,math,array
+expertise: intermediate
+firstSeen: 2022-09-07T05:00:00-04:00
+---
+
+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.
+
+```js
+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);
+};
+
+```
+
+```js
+maxSubarray(-2, 1, -3, 4, -1, 2, 1, -5, 4); // [4, -1, 2, 1]
+```