AlgoPlan0628

#largest permutation
#key idea:
- for each ascending sub-array in the big array, find the right most first downward slope, and swap it with the largest value on its right.
- if there is no such int, return original.
- it is called lexigraphically larger


class Solution {
    private int[] swap(int[] arr, int i ,int j ){
        int temp = arr[i];
        arr[i] = arr[j];
        arr[j] = temp;
        return arr;
    }
    public int[] prevPermOpt1(int[] arr) {
        int[] result = new int[arr.length];
        int left = arr.length-1;
        int right = 0;
        int largest = 0;
        for (; left >0; left--){
            if (arr[left]< arr[left-1]){
                //continue 
                //get the large one is left
                //from its right
                //get the second largest value
                right = left;
                largest = left-1;
                while (right < arr.length && arr[right]< arr[left-1]){
                    if (arr[right] !=arr[right-1]) largest = right;
                    right++;
                }
                System.out.println(left-1);
                System.out.println(largest);
                result = swap(arr,left-1,largest);
                return result;
            }else{
              //continue
            }
        }
        return arr;
    }
}