Difficulty:: Medium
Implement , which calculates x raised to the power n (xn).
Example 1:
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| Input: 2.00000, 10
Output: 1024.00000
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Example 2:
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| Input: 2.10000, 3
Output: 9.26100
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Example 3:
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| Input: 2.00000, -2
Output: 0.25000
Explanation: 2-2 = 1/22 = 1/4 = 0.25
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Note:
- -100.0 < x < 100.0
- n is a 32-bit signed integer, within the range [−231, 231 − 1]
Solution
Language: Java
位运算
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| class Solution {
public double myPow(double x, int n) {
if (x == 0) {
return 0;
}
if (n == 0) {
return 1;
}
long c = Math.abs((long) n);
double result = 1;
while (c > 0) {
if ((c & 1) == 1) {
result *= x;
}
x *= x;
c >>= 1;
}
return n < 0 ? 1 / result : result;
}
}
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递归
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| public class Solution {
public double pow(double x, int n) {
if(n == 0)
return 1;
if(n<0){
n = -n;
x = 1/x;
}
return (n%2 == 0) ? pow(x*x, n/2) : x*pow(x*x, n/2);
}
}
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递归麻烦版
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| class Solution {
public double myPow(double x, int n) {
if (x == 0) {
return 0d;
}
if (n == 0) {
return 1d;
}
if (n < 0) {
x = 1 / x;
n = -n;
}
return pow(x, n);
}
private double pow(double x, int n) {
if (n == 0) {
return 1d;
}
if (n == 1) {
return x;
}
if (n == 2) {
return x * x;
}
double tmp = pow(x, n / 2);
if (n % 2 == 0) {
return tmp * tmp;
} else {
return tmp * tmp * x;
}
}
}
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