USACO 2017 US Open Contest, Bronze Problem 1. The Lost Cow

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USACO2017-OPEN-B1

答案:

#include <iostream>
#include <cstdlib>

using namespace std;
typedef long long ll;

int main() {
ll x, y;
cin >> x >> y;

ll ans = 0;
ll by = 1;
ll dir = 1;
while(true) {
// dir == 1 means Farmer John is moving to the right, and
// dir == -1 means he is moving to the left.
if((dir==1 && x<=y && y<=x+by) || (dir==-1 && x-by<=y && y<=x)) {
// We found Bessie!
ans += abs(y-x);
cout << ans << endl;
break;
} else {
// Didn't find Bessie! Add to our running total the cost of
// moving 'by' units away from the start and back again.
// Then multiply our next move's length by 2 and switch direction.
ans += by*2;
by *= 2;
dir *= -1;
}
}
}