35 lines
1021 B
C++
35 lines
1021 B
C++
/** Let d(n) be defined as the sum of proper divisors of n (numbers less than n which divide evenly into n).
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If d(a) = b and d(b) = a, where a b, then a and b are an amicable pair and each of a and b are called amicable numbers.
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For example, the proper divisors of 220 are 1, 2, 4, 5, 10, 11, 20, 22, 44, 55 and 110; therefore d(220) = 284. The proper divisors of 284 are 1, 2, 4, 71 and 142; so d(284) = 220.
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Evaluate the sum of all the amicable numbers under 10000. */
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#include "0.hpp"
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#define _max 10000
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uu ami(uu x)
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{
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uu test = 1;
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uu sqr = (uu)(sqrt((double)x) + _eps);
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if(x == sqr * sqr) test += sqr;
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for(uu i = 2; i < sqr; i++)
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if(x % i == 0) {
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test += i + x / i;
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//cout << i << endl << x / i <<endl;
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}
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return test;
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}
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int main()
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{
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uu sum = 0;
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for(uu temp = 100; temp <= _max; temp++) {
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uu amip = ami(temp);
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if(temp == ami(amip) && temp - amip) {
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//cout << temp << '\t' << amip << endl;
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sum += amip + temp;
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}
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}
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cout << sum / 2 << endl;
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return 0;
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}
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