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copied!<p><strong>Edit: Solved!</strong></p> <p>You can create a generator that outputs the numbers in sorted order. There are a few rules for comparing concatenated strings that I think most of us know implicitly:</p> <ul> <li>a < a+b, where b is non-null.</li> <li>a+b < a+c, where b < c.</li> <li>a+b < c+d, where a < c, and a is not a subset of c.</li> </ul> <p>If you start with a sorted list of the first 1000 numbers, you can easily generate the rest by appending "thousand" or "million" and concatenating another group of 1000.</p> <p>Here's the full code, in Python:</p> <pre><code>import heapq first_thousand=[('', 0), ('one', 1), ('two', 2), ('three', 3), ('four', 4), ('five', 5), ('six', 6), ('seven', 7), ('eight', 8), ('nine', 9), ('ten', 10), ('eleven', 11), ('twelve', 12), ('thirteen', 13), ('fourteen', 14), ('fifteen', 15), ('sixteen', 16), ('seventeen', 17), ('eighteen', 18), ('nineteen', 19)] tens_name = (None, 'ten', 'twenty', 'thirty', 'forty', 'fifty', 'sixty', 'seventy','eighty','ninety') for number in range(20, 100): name = tens_name[number/10] + first_thousand[number%10][0] first_thousand.append((name, number)) for number in range(100, 1000): name = first_thousand[number/100][0] + 'hundred' + first_thousand[number%100][0] first_thousand.append((name, number)) first_thousand.sort() def make_sequence(base_generator, suffix, multiplier): prefix_list = [(name+suffix, number*multiplier) for name, number in first_thousand[1:]] prefix_list.sort() for prefix_name, base_number in prefix_list: for name, number in base_generator(): yield prefix_name + name, base_number + number return def thousand_sequence(): for name, number in first_thousand: yield name, number return def million_sequence(): return heapq.merge(first_thousand, make_sequence(thousand_sequence, 'thousand', 1000)) def billion_sequence(): return heapq.merge(million_sequence(), make_sequence(million_sequence, 'million', 1000000)) def solve(stopping_size = 51000000000): total_chars = 0 total_sum = 0 for name, number in billion_sequence(): total_chars += len(name) total_sum += number if total_chars >= stopping_size: break return total_chars, total_sum, name, number </code></pre> <p>It took a while to run, about an hour. The 51 billionth character is the last character of sixhundredseventysixmillionsevenhundredfortysixthousandfivehundredseventyfive, and the sum of the integers to that point is 413,540,008,163,475,743.</p>

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