[剑指offer] 其他算法[下]篇

JZ58 左旋转字符串

/* 模拟 */
public class JZ58_1
{
    public static String LeftRotateString(String str, int n)
    {
        if (str.length() == 0) return "";
        n %= str.length();
        return str.substring(n) + str.substring(0, n);
    }
}

/* 三次翻转 */
public class JZ58_2
{
    public static String LeftRotateString(String str, int n)
    {
        char[] strArr = str.toCharArray();
        int len = strArr.length;
        if (len == 0) return str;
        n = n % len;
        reverseStr(strArr, 0, n - 1);
        reverseStr(strArr, n, len - 1);
        reverseStr(strArr, 0, len - 1);
        return new String(strArr);
    }

    public static void reverseStr(char[] array, int begin, int end)
    {
        for (; begin < end; begin++, end--)
        {
            char c = array[begin];
            array[begin] = array[end];
            array[end] = c;
        }
    }
}

JZ62 孩子们的游戏(圆圈中最后剩下的数)

/* 约瑟夫环 */
public class JZ62_1
{
    public static int LastRemaining_Solution(int n, int m)
    {
        if (n == 1) return 0;
        else return (LastRemaining_Solution(n - 1, m) + m) % n;
    }
}

JZ75 字符流中第一个不重复的字符

/* 队列 + hash */
public class JZ75_2
{
    public static Queue<Character> queue = new LinkedList<>();
    public static HashMap<Character, Integer> map = new HashMap<>();

    public static void Insert(char ch)
    {
        if (!map.containsKey(ch))
            queue.add(ch);
        map.put(ch, map.getOrDefault(ch, 0) + 1);
    }

    public static char FirstAppearingOnce()
    {
        while (!queue.isEmpty())
        {
            if (map.get(queue.peek()) == 1)
                return queue.peek();
            else
                queue.poll();
        }
        return '#';
    }
}

/* 模拟 */
public class JZ75_1
{
    public static int[] num = new int[256];
    public static String str = "";

    public static void Insert(char ch)
    {
        str += ch;
        num[ch]++;
    }

    public static char FirstAppearingOnce()
    {
        for (char ch : str.toCharArray())
            if (num[ch] == 1)
                return ch;
        return '#';
    }
}

JZ14 剪绳子⭐

/* dfs + memo */
public class JZ14_1
{
    public static int[] table = new int[100];

    public static int cutRope(int n)
    {
        if (n == 0) return 1;
        if (table[n] != 0) return table[n];
        int res = -1;
        for (int i = 1; i <= n; i++)
            res = Math.max(res, i * cutRope(n - i));
        table[n] = res;
        return res;
    }
}

/* dp */
public class JZ14_2
{
    public static int cutRope(int n)
    {
        int[] dp = new int[n + 1];
        dp[1] = 1;
        dp[2] = 2;
        dp[3] = 3;
        for (int i = 4; i <= n; i++)
            for (int j = 1; j < i; j++)
                dp[i] = Math.max(dp[i], j * dp[i - j]);
        return dp[n];
    }
}

/*
 * 当 n>4 时,
 * 若将 n 分成 x 份,那么 (n/x)^(x) 最大时, x = e
 * 因为 x 为整数，所以 x 取 3
 * */
public class JZ14_3
{
    public static int cutRope(int n)
    {
        int res = 1;
        while (n > 4)
        {
            res *= 3;
            n -= 3;
        }
        return res * n;
    }
}

JZ81 调整数组顺序使奇数位于偶数前面(二)

/* 快排 */
public class JZ81_1
{
    public static int[] reOrderArrayTwo(int[] array)
    {
        if (array.length == 0) return array;
        int low = 0, high = array.length - 1;
        int pivot = array[high];
        while (low < high)
        {
            while (low < high && array[low] % 2 != 0) low++;
            array[high] = array[low];
            while (low < high && array[high] % 2 == 0) high--;
            array[low] = array[high];
        }
        array[low] = pivot;
        return array;
    }
}

/* 双指针 */
public class JZ81_2
{
    public static int[] reOrderArrayTwo(int[] array)
    {
        if (array.length == 0) return array;
        int low = 0, high = array.length - 1;
        while (low < high)
        {
            while (low < high && array[low] % 2 != 0) low++;
            while (low < high && array[high] % 2 == 0) high--;
            if (low < high)
            {
                int temp = array[low];
                array[low] = array[high];
                array[high] = temp;
            }
        }
        return array;
    }
}

JZ83 剪绳子（进阶版）

/* 与JZ14类似,使用快速幂 */
public class JZ83_1
{
    public static long MOD = 998244353;

    public static long cutRope(long number)
    {
        if (number == 2) return 1;
        if (number == 3) return 2;
        if (number == 4) return 4;
        long pow = (number - 5) / 3 + 1;
        System.out.println(pow);
        return (quick(3, pow) * (number - 3 * pow)) % MOD;
    }

    public static long quick(long n, long m)
    {
        long ans = 1;
        while (m != 0)
        {
            if (m % 2 != 0)
            {
                ans *= n;
                ans %= MOD;
            }
            n *= n;
            n %= MOD;
            m >>= 1;
        }
        return ans;
    }
}

JZ17 打印从1到最大的n位数

/* 模拟 */
public class JZ17_1
{
    public static int[] printNumbers(int n)
    {
        int top = (int) Math.pow(10, n);
        int[] res = new int[top - 1];
        for (int i = 1; i < top; i++)
            res[i - 1] = i;
        return res;
    }
}