日拱一卒

1 一周见闻

1.1 技术文章

1.2 泛互联网文章

2 技术总结

3 Algorithm(算法题)

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public boolean isSameTree(TreeNode p, TreeNode q) {
        if(p == null && q == null) {
            return true;
        } else if (p == null || q == null) {
            return false;
        } else if(p.val != q.val) {
            return false;
        } else {
            return isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
        }
    }
}

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public int maxDepth(TreeNode root) {
        if(root == null) {
            return 0;
        } else {
            int leftMax = maxDepth(root.left);
            int rightMax = maxDepth(root.right);
            return Math.max(leftMax, rightMax) + 1;
        }
    }
}

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public TreeNode invertTree(TreeNode root) {
        if(root == null) {
            return null;
        }
        TreeNode tmp = root.right;
        root.right = root.left;
        root.left = tmp;
        invertTree(root.left);
        invertTree(root.right);
        return root;
    }
}

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public boolean isSymmetric(TreeNode root) {
        if(root == null) {
            return true;
        }
        return isSymmetric(root.left, root.right);
    }

    public boolean isSymmetric(TreeNode left, TreeNode right) {
        if(left == null && right == null) {
            return true;
        }

        if(right == null || left == null) {
            return false;
        }
        if(left.val != right.val) {
            return false;
        }
        return isSymmetric(left.left, right.right) && isSymmetric(left.right, right.left);
    }


}

class Solution {
    public int findKthLargest(int[] nums, int k) {
        PriorityQueue<Integer> pq = new PriorityQueue<>();
        for (int e : nums) {
            pq.offer(e);
            if (pq.size() > k) {
                pq.poll();
            }
        }
        return pq.peek();
    }
}

class Solution {
    Random random = new Random();

    public int findKthLargest(int[] nums, int k) {
        return quickSelect(nums, 0, nums.length - 1, nums.length - k);
    }

    public int quickSelect(int[] a, int l, int r, int index) {
        int q = randomPartition(a, l, r);
        if (q == index) {
            return a[q];
        } else {
            return q < index ? quickSelect(a, q + 1, r, index) : quickSelect(a, l, q - 1, index);
        }
    }

    public int randomPartition(int[] a, int l, int r) {
        int i = random.nextInt(r - l + 1) + l;
        swap(a, i, r);
        return partition(a, l, r);
    }

    public int partition(int[] a, int l, int r) {
        int x = a[r], i = l - 1;
        for (int j = l; j < r; ++j) {
            if (a[j] <= x) {
                swap(a, ++i, j);
            }
        }
        swap(a, i + 1, r);
        return i + 1;
    }

    public void swap(int[] a, int i, int j) {
        int temp = a[i];
        a[i] = a[j];
        a[j] = temp;
    }
}

+912. 排序数组

class Solution {
    public int[] sortArray(int[] nums) {
        if (nums == null || nums.length == 1) {
            return nums;
        }
        quickSort(nums, 0, nums.length - 1);
        return nums;
    }

    private void quickSort(int[] nums, int l, int r) {
        if (l >= r) {
            return;
        }
        int q = randomPartition(nums, l, r);
        quickSort(nums, l, q - 1);
        quickSort(nums, q + 1, r);
    }

    private int partition(int[] nums, int l, int r) {
        int pivot = nums[r];
        int i = l;
        for (int j = l; j < r; j++) {
            if (nums[j] < pivot) {
                if (i == j) {
                    // 此时无需交换，两者相等
                    i++;
                } else {
                    swap(nums, i++, j);
                }
            }

        }
        swap(nums, i, r);
        return i;
    }

    private void swap(int[] nums, int i, int j) {
        int tmp = nums[i];
        nums[i] = nums[j];
        nums[j] = tmp;
    }

    private int randomPartition(int[] nums, int l, int r) {
        Random random = new Random();
        int pivotIndex = random.nextInt(r - l + 1) + l; // 随机选择划分点的索引
        swap(nums, pivotIndex, r); // 将划分点交换到数组末尾
        return partition(nums, l, r); // 调用普通的 partition 方法
    }

}