21544661

Posted 2021-09-08 保护眼睛

剑指offer

• • • 剑指 Offer 21. 调整数组顺序使奇数位于偶数前面
    • 剑指 Offer 54. 二叉搜索树的第k大节点
    • 剑指 Offer 46. 把数字翻译成字符串
    • 剑指 Offer 61. 扑克牌中的顺子

剑指 Offer 21. 调整数组顺序使奇数位于偶数前面

public class Solution21 {
    public static void main(String[] args) {
        System.out.println(Arrays.toString(exchange(new int[]{1, 2, 3, 4})));
    }

    public static int[] exchange(int[] nums) {
        int i = 0;
        int j = nums.length - 1;

        while (i < j) {
            while (i < j && nums[i] % 2 != 0) {
                i++;
            }
            while (i < j && nums[j] % 2 == 0) {
                j--;
            }
            int tmp = nums[i];
            nums[i] = nums[j];
            nums[j] = tmp;
        }

        return nums;
    }
}

剑指 Offer 54. 二叉搜索树的第k大节点

class TreeNode {
    int val;
    TreeNode left;
    TreeNode right;

    TreeNode(int val) {
        this.val = val;
    }
}

class Solution54 {
    PriorityQueue<Integer> priorityQueue = new PriorityQueue<>(new Comparator<Integer>() {
        @Override
        public int compare(Integer o1, Integer o2) {
            return o1 - o2;
        }
    });

    public int kthLargest(TreeNode root, int k) {
        preOrderTree(root);
        for (int i = 0; i < k - 1; i++) {
            priorityQueue.poll();
        }

        return priorityQueue.peek();
    }

    public void preOrderTree(TreeNode root) {
        if (root == null)
            return;

        priorityQueue.offer(root.val);
        preOrderTree(root.left);
        preOrderTree(root.right);
    }
}

class Solution54_2 {
    int k;
    int res;

    public int kthLargest(TreeNode root, int k) {
        this.k = k;
        dfs(root);
        return res;
    }

    public void dfs(TreeNode root) {
        if (root == null || k == 0)
            return;

        dfs(root.right);
        if (--k == 0)
            res = root.val;
        dfs(root.left);
    }
}

剑指 Offer 46. 把数字翻译成字符串

class Solution46 {
    public static int translateNum(int num) {
        if (num < 10) {
            return 1;
        }
        int tmp = num % 100;
        if (tmp < 10 || tmp >= 26) {
            return translateNum(num / 10);
        } else {
            return translateNum(num / 10) + translateNum(num / 100);
        }
    }

    public static void main(String[] args) {
        System.out.println(translateNum(12258));
    }
}

剑指 Offer 61. 扑克牌中的顺子

class Solution61 {
    public static void main(String[] args) {
        System.out.println(isStraight(new int[]{0, 0, 8, 5, 4}));
    }

    public static boolean isStraight(int[] nums) {
        Arrays.sort(nums);
        int count = 0;
        int sub = 0;
        for (int i = 0; i < 4; i++) {
            if (nums[i] == 0) {
                count++;
                continue;
            }
            if (nums[i + 1] == nums[i]) return false;
            sub += (nums[i + 1] - nums[i] - 1);
        }

        return sub <= count;
    }
}