剑指 Offer 49. 丑数

public int nthUglyNumber(int n) {
        int a = 0,b = 0,c = 0;
        int[] dp = new int[n];
        dp[0] = 1;
        for(int i = 1;i<n;i++){
            int n2 = dp[a]*2,n3 = dp[b]*3,n5 = dp[c]*5;
            dp[i] = Math.min(Math.min(n2,n3),n5);
            if(dp[i] == n2) a++;
            if(dp[i] == n3) b++;
            if(dp[i] == n5) c++;
        }
        return dp[n-1];
    }