209. Minimum Size Subarray Sum

// brute force approach(It would give you TLE)
class Solution {

    public boolean helper(int target, List<Integer> list) {
        int sum = 0;
        for(int i = 0; i < list.size(); i++) {
            sum += list.get(i);
        }
        if(sum >= target) {
            return true;
        }
        return false;
    }

    public int minSubArrayLen(int target, int[] nums) {
        int mini = Integer.MAX_VALUE;
        for(int i = 0; i < nums.length; i++) {
            List<Integer> list = new ArrayList<>();
            for(int j = i; j < nums.length; j++) {
                list.add(nums[j]);
                if(helper(target, list)) {
                    mini = Math.min(list.size(), mini);
                }
                
            }
        }
        if(mini == Integer.MAX_VALUE) return 0;

        return mini;
    }
}


// binary search (better technique to solve this problem)

class Solution {
      public boolean slidingWindow(int k, int[] nums, int target) {

      int sum = 0;
      for(int i = 0; i < k; i++) {

         sum += nums[i];
      }
      if(sum >= target) {
         return true;
      }
      int pointer = 0;
      for(int i = k; i < nums.length; i++) {
         sum += nums[i];
         sum -= nums[pointer++];
         if(sum >= target) {
            return true;
         }
      }
      return false;
   }
   public int binary_search(int[] nums, int target) {
      int mini = Integer.MAX_VALUE;
      int start = 1;
      int end = nums.length;
      while (start <= end) {
         int mid = (start + end) / 2;
         if(slidingWindow(mid, nums, target)) {
            mini = Math.min(mini, mid);
            end = mid - 1;
         }
         else {
            start = mid + 1;
         }
      }
      if(mini == Integer.MAX_VALUE) {
         return 0;
      }
      return mini;
   }

    public int minSubArrayLen(int target, int[] nums) {
        return binary_search(nums, target);
    }
}


// sliding window (optimal technique to solve this problem)

class Solution {
    public int minSubArrayLen(int target, int[] nums) {
        int sum = 0;
        int pointer = 0;
        int mini = Integer.MAX_VALUE;
        for(int i = 0; i < nums.length; i++) {
            sum += nums[i];
            while (sum >= target) {
                sum -= nums[pointer];
                mini = Math.min(mini, i - pointer + 1);
                pointer++;
            }
        }
        if(mini == Integer.MAX_VALUE) return 0;

        return mini;
    }
}