Traversing Two Collections at Once

Some problems need two collections read together, not one at a time. If names[i] and scores[i] describe the same person, you don't want two separate loops — you want one index i that steps through both arrays at once, so each iteration gives you a matched pair. The loop counter does double duty: it's a position in names and the same position in scores, simultaneously.

The mechanism is just a single for loop: for (int i = 0; i < length; i++), and inside it you reference both collections with that same i — names.get(i) alongside scores.get(i), or names[i] alongside scores[i]. To find the top scorer, track a running maximum and the index where it occurred, updating both whenever scores[i] beats the current best. To check if two arrays are equal, walk both with one i and compare array1[i] to array2[i] at every step, stopping and returning false the moment a mismatch shows up; if the loop finishes with no mismatches, they're equal.

This builds directly on single-collection traversal from earlier in the unit — same shifting-index idea, just driving two collections instead of one. It also sets up more complex multi-structure work later, like comparing rows of a 2D array or merging two sorted lists, where keeping indices aligned (or handling them when they can't stay aligned) becomes the whole problem.