Mastering Sliding Windows

The sliding window pattern is used to reduce nested loops ($O(N^2)$) to a single pass ($O(N)$) when processing contiguous sequences of arrays or strings. The window is defined by two boundaries: a left pointer and a right pointer.

Fixed vs Variable Sliding Window

In a fixed window, the difference between the right and left pointers is constant. In a variable window, the boundaries expand or shrink based on constraints, such as unique character limits.

function minSubArrayLen(target, nums) {
    let minLength = Infinity;
    let left = 0;
    let sum = 0;
    
    for (let right = 0; right < nums.length; right++) {
        sum += nums[right];
        
        while (sum >= target) {
            minLength = Math.min(minLength, right - left + 1);
            sum -= nums[left];
            left++;
        }
    }
    return minLength === Infinity ? 0 : minLength;
}