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Code2:
Analysis
At first glance, both pieces of code are three-level nested for loops, each iterating 100 * 1000 * 1000 times.
So there should be no difference in performance?
Wait, wait, wait, be careful. The nesting order of the for loops of these two code pieces is actually different. In the first code, the outermost for loop executes 100 times and the innermost for loop executes 10,000 times. In the second code , on the other hand, executes the outermost for loop 10,000 times and the innermost for loop 100 times.
Does such a subtle difference affect the performance of the program?
Answer
We can execute these two code pieces directly in the browser console, and this is the result:
When we actually execute these two pieces of code, we can find that there is a significant difference in the time consumed by the two. The first code took 287 milliseconds, and the second code took 455 milliseconds. Such an obvious difference cannot be explained by random error.
Why is there such a difference? In fact, we only need to do a simple math problem:
In these two pieces of code, how many times are j, k, l, x, y, and z initialized respectively? How many times do they performed auto-increment operations?
For example, the variable j is the outermost for loop variable. It will only be initialized…
