The patterns behind countless interview problems — two pointers, sliding windows, monotonic stacks and more — animated step by step.
Finds the contiguous subarray with the largest sum in a single pass. Works with negative numbers by restarting the running window whenever it would only drag the total down.
On a sorted array, finds two values that add up to a target using a pointer at each end — moving them inward based on whether the current sum is too small or too large.
Finds the maximum sum of any K consecutive elements. Instead of re-adding the whole window each time, it slides one step — subtracting the element that leaves and adding the one that enters.
Partitions an array into three regions — less than, equal to, and greater than a pivot — in one pass with three pointers. The classic problem of sorting an array of 0s, 1s, and 2s.
Computes how much water is trapped between bars of an elevation map. Two pointers walk inward from both ends, resolving the shorter side first since its limiting wall is already known.
For each element, finds the first larger value to its right using a monotonic stack of indices that are still waiting for their answer. Each index is pushed and popped at most once.