LeetCode（剑指 Offer）- 49. 丑数

Posted 2022-04-15 放羊的牧码

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题目大意：略

解题思路：略

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AC 代码

• Java

// 枚举暴力（超时）
class Solution 
    public int nthUglyNumber(int n) 
        int num = 1, res = -1;
        for (int i = 0; i < n;) 
            if (isUglyNum(num)) 
                res = num;
                i++;
            
            num++;
        
        return res;
    

    private boolean isUglyNum(int num) 
        while (num % 2 == 0) 
            num /= 2;
        

        while (num % 3 == 0) 
            num /= 3;
        

        while (num % 5 == 0) 
            num /= 5;
        

        return num == 1;
    


// AC
class Solution 
    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];
    

• C++

class Solution 
public:
    int nthUglyNumber(int n) 
        int a = 0, b = 0, c = 0;
        int dp[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] = min(min(n2, n3), n5);
            if(dp[i] == n2) a++;
            if(dp[i] == n3) b++;
            if(dp[i] == n5) c++;
        
        return dp[n - 1];
    
;