劍指offer____醜數
阿新 • • 發佈:2018-11-11
把只包含質因子2、3和5的數稱作醜數(Ugly Number)。例如6、8都是醜數,但14不是,因為它包含質因子7。 習慣上我們把1當做是第一個醜數。求按從小到大的順序的第N個醜數。
方法一:
class Solution { public: bool IsUgly(int num) { while(num % 2 == 0) num /= 2; while(num % 3 == 0) num /= 3; while(num % 5 == 0) num /= 5; return (num == 1) ? true:false; } int GetUglyNumber_Solution(int index) { if(index <= 0) return -1; // if(index == 1) return 1; int count = 0; int number = 0; while(count < index) { number++; if(IsUgly(number)) { count++; } } return number; } };
方法二:
class Solution { public: int Min(int num1,int num2,int num3) { int min = num1 < num2 ? num1:num2; min = min < num3 ? min:num3; return min; } int GetUglyNumber_Solution(int index) { if(index <= 0) return 0; int *p = new int [index]; p[0] = 1; int nextInd = 1; int *p2 = p; int *p3 = p; int *p5 = p; while(nextInd < index) { int min = Min(*p2 *2,*p3 *3,*p5*5); p[nextInd] = min; while(*p2 * 2 <= p[nextInd]) p2++; while(*p3 * 3 <= p[nextInd]) p3++; while(*p5 * 5 <= p[nextInd]) p5++; ++nextInd; } int ugly = p[nextInd - 1]; delete []p; return ugly; } };