剑指 Offer.49-丑数

class Solution {
    public int nthUglyNumber(int n) {
        int[] dp = new int[n];
        // 声明3个坐标,乘以三个质因子
        int a = 0 ,b = 0,c = 0;
        dp[0] = 1;  
        for(int i=1;i<n;i++){
            int xa = dp[a]*2;
            int xb = dp[b]*3;
            int xc = dp[c]*5;
            dp[i] = Math.min(Math.min(xa,xb),xc);
            if(xa == dp[i]) a++;
            if(xb == dp[i]) b++;
            if(xc == dp[i]) c++;
        }
        return dp[n-1];
    }
}