Solutions to Cracking the Coding Interview 6th edition.
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# Cracking the Coding Interview

## I - VII

• Quick sort picks a random element as a “pivot” and then swaps values in the array such that the elements less than pivot appear before elements greater than pivot. This gives a “partial sort:‘Then it recursively sorts the left and right sides using a similar process.

• How do you describe the runtime of insertion? This is a tricky question. The array could be full. If the array contains N elements, then inserting a new element will take O(N) time. You will have to create a new array of size 2N and then copy N elements over. This insertion will take O ( N) time. However, we also know that this doesn’t happen very often. The vast majority of the time insertion will be in O(l) time.

• In binary search, we are looking for an example x in an N-element sorted array. We first compare x to the midpoint of the array. If x == middle, then we return. If x < middle, then we search on the left side of the array. If x > middle, then we search on the right side of the array.

• This is a good takeaway for you to have. When you see a problem where the number of elements in the problem space gets halved each time, that will likely be a 0( log N) runtime.

• Here’s a tricky one. What’s the runtime of this code? Very interesting 3. example!

• The following simple code sums the values of all the nodes in a balanced binary search tree. What is its runtime? Very interesting 9. example!

• Very interesting 11. example! Not factorial but O(n) time for calculating factorial.

• Don’t get fooled by naming!

• Is there anything else that is unnecessary? Yes. If there’s onl one valid d value for each (a, b, c), then we can just compute it. This is just simple math: d = a + b - C • This will reduce our runtime from O(N 4 ) to O(N 3 ).

• This is another place where BCR can be useful. Any work you do that’s less than or equal to the BCR is “free;’ in the sense that it won’t impact your runtime. You might want to eliminate it eventually, but it’s not a top priority just yet.

## VIII

### 1

• A hash table is a data structure that maps keys to values for highly efficient lookup.

• If the number of collisions is very high, the worst case runtime is O(N), where N is the number of keys. However, we generally assume a good implementation that keeps collisions to a minimum, in which case the lookup time is 0(1).

• On each concatenation, a new copy of the string is created, and the two strings are copied over, character by character. The first iteration requires us to copy x characters. The second iteration requires copying 2x characters. T he third iteration requires 3x, and so on. The total time therefore is O( x + 2x + . . . + nx). This reduces toO(xn 2 ). That is because 1 + 2 + ... + n = n * (n - 1) / 2. And it happens because of the non-resizing array. Use string builders for resizable array and complexity of O(n).