出现错误的 QuickSort Java 代码超出时间限制

Question

I am using the below code to sort out a given array using Quick Sort Algo. I am a beginner and am struggling to understand why my code runs fine on few test cases but fails on few. I am receiving error Time Limit Exceeded. The code is constantly failing the test case :- array{5,5,6,8,4,5,6} . Feel free to give tips on how to code better.

        public static void quickSort(int[] input) {
            quickSort(input, 0 , input.length-1) ;   
        }
        public static void quickSort(int input[] , int startIndex , int endIndex) {
            if(startIndex >= endIndex){
                 return;
            } else{
            int pivot = partition(input, startIndex , endIndex);
            quickSort(input,startIndex , pivot-1) ; 
            quickSort(input , pivot+1 , endIndex) ;
            }
        }

        public static int partition(int input[] ,int startIndex , int endIndex) {
            int pivot = input[startIndex] ; 
            int count  = 0; 
            for(int i = 1+startIndex ; i < input.length ; i++){
                if(input[i] < pivot){
                    count++;
                }
            }
            input[startIndex] = input[startIndex+count]; 
            input[startIndex+count] = pivot ;

            int s = startIndex ; 
            int e = endIndex ;
            int sc = startIndex+count;

            while(s < sc &&  sc < e){
                if(input[s] < pivot) {
                    s++;
                } else if(input[e] >= pivot){
                    e--;
                }else if(input[s] > pivot && input[e] < pivot){
                    int temp = input[e];
                    input[e] = input[s] ; 
                    input[s] = temp;
                    e--;
                    s++;
                    }
            }     
        return sc;
        }    
    }

Answer 1

At a glance it seems you're using the indexes as a way to indicate subarray limits

        public static int partition(int input[] ,int startIndex , int endIndex)

But then you iterate the whole array always ( the condition is i < input.length ) on:

for(int i = 1+startIndex ; i < input.length ; i++){
   if(input[i] < pivot){
     count++;
   }
 ...

So in your subsequent iterations you're still going through the whole array:

So in this call:

quickSort(input,startIndex , pivot-1);

pivot -1 is ignored as you go through input.length anyway causing the guard condition:

if (startIndex >= endIndex )

to never evaluate to true hence running forever.

Try changing your for loop to (didn't try this myself, just by looking at the code):

for(int i = 1+startIndex ; i < endIndex ; i++){

And see if that works.

I hope this helps.