What is this all about?
- Used for searching pairs in a SORTED array
- Create pointers that correspond to an index and move towards the beginning, end or middle based on a certain condition.
- We are able to process two or more elements per loop instead of just one.
When do we use it?
- In many problems involving collections such as arrays or lists, we have to analyze each element of the collection compared to its other elements.
Common patterns
- Two pointers, each starting from the beginning and the end until they both meet.
- One pointer moving at a slow pace, while the other pointer moves at twice the speed.
--- Problem We are asked to compare two elements in an ordered array. --- FOOR LOOP If we use a for loop, we create an external pointer and use the internal "j" as the second pointer. var i = 0; for(var j = 1; j < array.length; j++){ if(arr[i] !== arr[j]){ i++; arr[i] = arr[j] } --- WHILE LOOP If we use a while loop we create two external pointers and the base one case is while left<right {}. This structure is used when we need to traverse the array from two opposite points. let left = 0 <-- pointer 1 let right = array.length - 1 <-- pointer 2 while (left < right) { let average = array[left] + array[right] / 2 if (average === target) return true; else if(average < target) left++ else right-- } return false } In action
Implement a function called countUniqueValues, which accepts a sorted array, and counts the unique values in the array.
Code to resolve this:
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