In an full stack application with high traffic, what would you do to make the application highly efficient

If some of your REST endpoints are slow and not behaving normal, how would you diagnose the problem, and how would you fix it.

Solve this coding problem: /** * Give an array of integers, which might containt 0, 1, 2, .. 0 can be repeated. * shift the non-zero elements at the beginning of the array, and maintain the order. * 0, 1, 0, 3, 12 * the final array should be like this: * 1, 3, 12, 0, 0 */