CPU time limit and Heap Size issues in Salesforce

 CPU time limit and Heap Size issues are two of the notorious governor limits.

How do you debug and figure out where exactly the CPU time or heap size is consumed?

Use limit statements in your code 

Limits. getHeapSize() and Limits.getCPUTime()

Add these statements in multiple places to debug the flow and figure out where exactly the time or heap size is consumed.