题目大意：给出x，求一个e，使得x * 10 ^ y ≤ 2 ^ e < (x + 1) * 10 ^ y。
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解题思路：问题可以转换成log2(x) + y * log2(10) ≤ e < log2(x + 1) + y*log2(10),
然后枚举y，判断条件。
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#include
#include
#include
int main () {
int x, y;
double l, r, d, a, b;
while (scanf("%d", &x) == 1) {
y = x;
int c = 0;
while (y) {
c++;
y /= 10;
}
l = log(x) / log(2);
r = log(x + 1) / log(2);
d = log(10) / log(2);
for (int i = c + 1; ; i++) {
a = l + i * d;
b = r + i * d;
if (ceil(a) <= floor(b)) {
printf("%.0lf\n", ceil(a));
break;
} else if (i == 1000000) {
printf("no power of 2\n");
break;
}
}
}
return 0;
}
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