Recursion
Learn to think recursively — base case plus recursive case, the call stack, recursion trees, and the patterns (linear, binary, divide-and-conquer, backtracking) that show up everywhere in contest problems.
Learn to think recursively — base case plus recursive case, the call stack, recursion trees, and the patterns (linear, binary, divide-and-conquer, backtracking) that show up everywhere in contest problems.