LeetCode Weekly Contest 24

https://leetcode.com/contest/...

01 Matrix

Given a matrix consists of 0 and 1, find the distance of the nearest 0 for each cell.
The distance between two adjacent cells is 1.
Example 1:
Input:
0 0 0
0 1 0
0 0 0
Output:
0 0 0
0 1 0
0 0 0

1. Learn How to use chan as Queue in Golang

2. Initially, I was trying to BFS every 1 to find the nearest 0, Timeout O(n^3); then change to start from every 0 to update all the
   1s, cut it when encounter any disi < nowDis, still O(n^3)

3. Put all 0 in Queue as initial, BFS when find a new updating also put it into Queue, as this we can guarantee the accurate within
   O(n^2)

func InitData(matrix [][]int) [][]int {
        data := make([][]int, 0)
        for index, list := range matrix {
                data = append(data, make([]int, 0))
                for _, item := range list {
                        if 0 == item {
                                data[index] = append(data[index], 0)
                        } else {
                                data[index] = append(data[index], -1)
                        }
                }
        }
        return data
}

type Node struct {
        X int
        Y int
        V int
}

const MAX_N = 10001
var queue = make(chan Node, MAX_N)
var Dir = [][]int{{0, 1}, {0, -1}, {1, 0}, {-1, 0}}

func Inrange(x, y int, matrix [][]int) bool {
        if x < 0 || y < 0 || x >= len(matrix) || y >= len(matrix[x]) {
                return false
        }
        return true
}

func bfs(data [][]int) {
        //fmt.Printf("%v %v,  data[%v]\n", x, y, data)
        for ir, list := range data {
            for ic, item := range list {
                        if 0 == item {
                            queue <- Node{X: ir, Y: ic, V: 0}
                        }
                }
        }
        
        node := Node{}
        for  {
                select {
                        case node = <-queue:
                        default: return
                }
                
                //fmt.Printf("node %v, min[%v] %v\n", node, min, len(queue))
                for _, dir := range Dir {
                        nx := node.X + dir[0]
                        ny := node.Y + dir[1]
                        if false == Inrange(nx, ny, data) {
                                continue
                        }
                        
                        if -1 != data[nx][ny] && data[nx][ny] <= node.V + 1 {
                            continue
                        }

                        data[nx][ny] = node.V + 1
                        queue <- Node{X: nx, Y: ny, V: node.V + 1}
                        //fmt.Printf("-- %v %v, min%v\n", nx, ny, min)
                }
        }

        return
}

func updateMatrix(matrix [][]int) [][]int {
        data := InitData(matrix)

        bfs(data)
        return data
}

---

Convert BST to Greater Tree

https://leetcode.com/contest/...
Given a Binary Search Tree (BST), convert it to a Greater Tree such that every key of the original BST is changed to the original key plus sum of all keys greater than the original key in BST.

Example:

Input: The root of a Binary Search Tree like this:

5
        /   \
       2     13

Output: The root of a Greater Tree like this:

18
        /   \
      20     13

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */

var totalSum int

func dfs(node *TreeNode) {
    if nil != node.Right {
        dfs(node.Right)
    }

    nodeVal := node.Val
    node.Val += totalSum
    totalSum += nodeVal

    if nil != node.Left {
        dfs(node.Left)
    }
}

func convertBST(root *TreeNode) *TreeNode {
    totalSum = 0
    if nil != root {
        dfs(root)
    }
    return root
}

---

Diameter of Binary Tree

Given a binary tree, you need to compute the length of the diameter of the tree. The diameter of a binary tree is the length of the longest path between any two nodes in a tree. This path may or may not pass through the root.

Example:
Given a binary tree

1
     / \
    2   3
   / \     
  4   5

Return 3, which is the length of the path [4,2,1,3] or [5,2,1,3].

Note: The length of path between two nodes is represented by the number of edges between them.

/**
 * Definition for a binary tree node.
 * type TreeNode struct {
 *     Val int
 *     Left *TreeNode
 *     Right *TreeNode
 * }
 */

var maxDia int 
 
func dfs(node *TreeNode) int {
    leftDia := 0
    rightDia := 0
    if nil != node.Left {
        leftDia = dfs(node.Left)
    }
    if nil != node.Right {
        rightDia = dfs(node.Right)
    }
    
    if (leftDia + rightDia > maxDia) {
        maxDia = leftDia + rightDia
    }
    
    if leftDia > rightDia {
        return leftDia+1
    } else {
        return rightDia+1
    }
} 
 
func diameterOfBinaryTree(root *TreeNode) int {
    maxDia = 0
    if nil != root {
        dfs(root)
    }
    return maxDia
}