Kotlin每日打卡（DFS+剪枝）：``` class Solution { fun hasValidPath(grid: Array<CharArray>): Boolean { val m = grid.size val n = grid[0].size if ((m + n) % 2 == 0 || grid[0][0] == ')' || grid[m - 1][n - 1] == '(

Kotlin每日打卡（组合数学，固定个位偶数，分别处理十位非零，最后处理百位非零）：``` class Solution { fun totalNumbers(digits: IntArray): Int { val digitCounts = IntArray(10) for (digit in digits) { digitCounts[digit]++ } var totalNonZeroT

Kotlin每日打卡（二叉树dfs）：``` /** * Example: * var ti = TreeNode(5) * var v = ti.`val` * Definition for a binary tree node. * class TreeNode(var `val`: Int) { * var left: TreeNode? = null * var right: TreeNo

Kotlin每日打卡（贡献法）：``` class Solution { fun countCommas(n: Long): Long { var ans = 0L var i = 1000L while (i <= n) { ans += (n - i + 1) i *= 1000 } return ans } }