LeetCode: 969. Pancake Sorting
Given an array A, we can perform a pancake flip: We choose some positive integer k <= A.length, then reverse the order of the first k elements of A. We want to perform zero or more pancake flips (doing them one after another in succession) to sort the array A.
Return the k-values corresponding to a sequence of pancake flips that sort A. Any valid answer that sorts the array within 10 * A.length flips will be judged as correct.
Example:
Input: [3,2,4,1]
Output: [4,2,4,3]
Explanation:
We perform 4 pancake flips, with k values 4, 2, 4, and 3.
Starting state: A = [3, 2, 4, 1]
After 1st flip (k=4): A = [1, 4, 2, 3]
After 2nd flip (k=2): A = [4, 1, 2, 3]
After 3rd flip (k=4): A = [3, 2, 1, 4]
After 4th flip (k=3): A = [1, 2, 3, 4], which is sorted.
Example:
Input: [1,2,3]
Output: []
Explanation: The input is already sorted, so there is no need to flip anything.
Note that other answers, such as [3, 3], would also be accepted.
Note:
- <= A.length <= 100
- A[i] is a permutation of [1, 2, …, A.length]
My Solution (Kind of Brute Force, but only spend half hour :) )
/**
* @param {number[]} A
* @return {number[]}
*/
var pancakeSort = function(A) {
var sortArray = [];
//i numbers in A
for(var i = 0; i < A.length; i++){
//find largest number in array
var n = 0;
var largeNum = A.length - i;
while(A[n] < largeNum){ n++; }
//reverse twice
for(var m = 0; m < n/2; m++){
var b = A[m];
A[m] = A[n - m];
A[n - m] = b;
}
for(var m = 0; m < largeNum/2; m++){
var b = A[m];
A[m] = A[largeNum - 1 - m];
A[largeNum - 1 - m] = b;
}
sortArray.push(n + 1);
sortArray.push(largeNum);
}
return sortArray;
};