2 つのポインターとスライディング ウィンドウのパターン

public class Sample{
    public static void main(String args[]){
        n = 10;
        int arr[] = new int[n];

        //Brute force approach for finding the longest subarray with sum <=k
        //tc : O(n^2)
        int maxlen=0;
        for(int i =0;i<arr.length;i++){
            int sum =0;
            for(int j = i+1;j<arr.length;j++){
                sum+=arr[j];
                if(sum<=k){
                    maxLen = Integer.max(maxLen, j-i+1);
                }
                else if(sum > k) break; /// optimization if the sum is greater than the k, what is the point in going forward? 
            }
        }

        //O(n+n) in the worst case r will move from 0 to n and in the worst case left will move from 0 0 n as well so 2n
        int left = 0;
        int right =0;
        int sum = 0;
        int maxLen = 0;
        while(right<arr.length){
            sum+=arr[right];
            while(sum > k){
                sum = sum-arr[left];
                left++;
            }
            if(sum <=k){
                maxLen = Integer.max(maxLen, right-left+1); //if asked to print max subarray length,we print maxLen else asked for printing the subarray keep track of
                // left and right in a different variable 
            }
            right++;
        }

        int right =0;
        int sum = 0;
        int maxLen = 0;
        while(right<arr.length){
            sum+=arr[right];
            if(sum > k){// this will ensure that the left is incremented one by one (not till the sum<=k because this might reduce the length i.e right-left+1  which will not be taken into consideration)
                sum = sum-arr[left];
                left++;
            }
            if(sum <=k){
                maxLen = Integer.max(maxLen, right-left+1); //if asked to print max subarray length,we print maxLen else asked for printing the subarray keep track of
                // left and right in a different variable 
            }
            right++;
        }

    }
}