CareerCup calculate (x^y)%z without pow();

转载于 2014-02-28 16:40:47 发布 · 797 阅读

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本文介绍了一种使用二进制加权幂运算方法实现的快速幂取模算法，该算法可以将复杂度从O(y)降低到O(log y)，特别适用于大数幂运算场景。

calculate (x^y)%z without pow();

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the question here is how we can reduce the complexity... if we compute the x^y by normal method the complexity is O(y)... to reduce the complexity we can use binary weighted power computation method in which complexity is O(logy)..

ans=1;
square=x;
if(y==0)
    return 1;
while(y!=0)
{
    if(y%2)
        ans=ans*square;
    square=(square*square)%z;
    y=y/2;
    if(ans>z)
        ans=ans%z;
}
return ans;