标签:return helper int double 50 res solution Pow
This problem is very easy to solve if using bruteforece solution, the time complexity is O(n).
public double myPow(double x, int n) { if (n == 0) return 1; double res = 1; int m = Math.abs(n); for (int i = 0; i < m; i++) { res *= x; } if (n > 0) return res; else return 1 / res; }
But this will caused a TLE, so we need to think about a O(logn) solution:
1. When the m is an even number, we make x = x*x, m = m/2;
2. When the m is an odd number, we need to multiple an extra x with res.
3. The m is odd number will must happen if m!=0, because m must be 1 at last.
public double myPow_Iteration(double x, int n) { double res = 1; int m = n; while (m != 0) { if (m % 2 != 0) res *= x; x *= x; m /= 2; } if (n >= 0) return res; else return 1 / res; }
The Recursive solution with the same time complexity with Iteration solution is:
public double myPow(double x, int n) { double res = helper(x, n); if (n < 0) return 1 / res; else return res; } private double helper(double x, int n) { if (n == 0) return 1; if (n % 2 == 0) { return helper(x * x, n / 2); } else { return x * helper(x * x, n / 2); //when n==1, this line will be executed, and return x*1; } }
标签:return,helper,int,double,50,res,solution,Pow 来源: https://www.cnblogs.com/feiflytech/p/15862425.html
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