Word ladder: code to surf, step by step
Word ladder: code to surf asks for a path made of single letter changes. The starting word is code, the destination is surf, and the requested length is four steps. Try arranging that path before reading the completed sequence below. The useful thing to track is the relationship between neighboring words: each move needs a single changed letter, with the remaining letters kept in their places. A path can be read as a series of small choices, each of which can be checked on its own.
The complete Word ladder solution is code -> core -> sore -> sure -> surf. The chain contains the starting word, the intermediate words, and the destination; the four steps are the transitions between them. Compare code with surf letter by letter before inspecting those transitions. Every position differs between the endpoints, so every position needs attention somewhere along the path. In this solution, each position changes once. The intermediate words make it possible to place those changes in a particular order while keeping each transition within the single letter rule. The order is part of the solution, so it helps to keep the whole sequence visible during the check.
Begin with code and change the third letter from d to r. That produces core, the first intermediate word. The letters that stay in place are c in the first position, o in the second position, e in the fourth position. Reading the pair side by side makes the change easy to isolate: focus on the changed position, then check the positions around it. This opening move places one of the destination letters into the starting pattern. It also supplies the word from which the next move begins. Keep both parts of that check in view, the single substitution and the resulting word, before moving onward.
The next move takes core to sore, changing the first letter from c to s. The retained letters are o in the second position, r in the third position, e in the fourth position. This comparison uses the word produced by the previous move as its starting point. Treat the pair as a fresh local check, then reconnect it to the sequence already established. The earlier substitution remains in place while another position receives its destination letter. At this point, sore is the word to carry forward. There is no need to combine the changes into one jump; their separation is what makes the path satisfy the stated instruction.
The third move changes sore to sure, replacing o with u in the second position. The fourth move changes sure to surf, replacing e with f in the fourth position. These remaining changes bring the path to surf. Each pair still keeps all positions except the changing one intact. As the path closes, compare the last word with the requested destination, then count the transitions from the start. Reaching the destination and using the requested number of steps are separate checks, and both can be read directly from the chain. That final review ties the individual substitutions back to the original question.
Reading this Word ladder backward offers another way to inspect the same relationships: surf -> sure -> sore -> core -> code. The direction changes, but each neighboring pair still differs at a single position. Use this backward reading as a check on the completed path, beginning with the destination and returning through the intermediate words. It can also guide an approach to the puzzle: consider a word next to the destination, then ask how the starting word might connect to it. The forward and backward readings meet in the same sequence. Neither reading needs an extra substitution, and both keep the changed positions easy to follow.
A general Word ladder method follows from these checks. Write the endpoints side by side, mark the positions that differ, and consider which single substitution can form the next word. After choosing a candidate, compare it with the current word before extending the path. For this solution, the positions change in this order: third, then first, then second, then fourth. Keep a record of the transitions so the step count remains visible. If a candidate requires several letters to change together, set it aside and consider a single position instead. Work toward a complete sequence that can be checked one neighboring pair at a time.
To finish reviewing the Word ladder, return to code and trace the substitutions all the way to surf. Read each intermediate word as both the result of one move and the starting point of the next. That perspective keeps the links connected without hiding their individual changes. The result is a path of four single letter steps, with every endpoint difference addressed once. For a final practice pass, cover the intermediate words and reconstruct the path from the endpoints. Then uncover the sequence and compare each transition. The useful takeaway is the method: separate the positions, build the links, and check the finished path.