原文地址：http://www.javashuo.com/article/p-biugusbt-s.html html
Given a non-negative integer num represented as a string, remove k digits from the number so that the new number is the smallest possible.git
Note:app
Example 1:less
Input: num = "1432219", k = 3 Output: "1219" Explanation: Remove the three digits 4, 3, and 2 to form the new number 1219 which is the smallest.
Example 2:spa
Input: num = "10200", k = 1 Output: "200" Explanation: Remove the leading 1 and the number is 200. Note that the output must not contain leading zeroes.
Example 3:code
Input: num = "10", k = 2 Output: "0" Explanation: Remove all the digits from the number and it is left with nothing which is 0.
给定一个以字符串表示的非负整数 num，移除这个数中的 k 位数字，使得剩下的数字最小。orm
注意:htm
示例 1 :blog
输入: num = "1432219", k = 3 输出: "1219" 解释: 移除掉三个数字 4, 3, 和 2 造成一个新的最小的数字 1219。
示例 2 :three
输入: num = "10200", k = 1 输出: "200" 解释: 移掉首位的 1 剩下的数字为 200. 注意输出不能有任何前导零。
示例 3 :
输入: num = "10", k = 2 输出: "0" 解释: 从原数字移除全部的数字，剩余为空就是0。
40ms
1 class Solution { 2 func removeKdigits(_ num: String, _ k: Int) -> String { 3 let n = num.count 4 if n == k { return "0" } 5 var k = k 6 var stack: [Character] = [] 7 let ca = Array(num) 8 for i in 0..<n { 9 while k > 0 && !stack.isEmpty && stack.last! > ca[i] { 10 stack.removeLast() 11 k -= 1 12 } 13 stack.append(ca[i]) 14 } 15 16 while k > 0 { 17 stack.removeLast() 18 k -= 1 19 } 20 21 while !stack.isEmpty && stack[0] == "0" { 22 stack.removeFirst() 23 } 24 25 return stack.isEmpty ? "0" : String(stack) 26 } 27 }
44ms
1 class Solution { 2 func removeKdigits(_ num: String, _ k: Int) -> String { 3 var stack = [Character]() 4 var removed = 0 5 for digit in num { 6 while removed < k && !stack.isEmpty && digit < stack.last! { 7 stack.removeLast() 8 removed += 1 9 } 10 stack.append(digit) 11 } 12 while removed < k { 13 stack.removeLast() 14 removed += 1 15 } 16 stack = stack.reversed() 17 while let last = stack.last, last == Character("0") { 18 stack.removeLast() 19 } 20 guard !stack.isEmpty else { 21 return "0" 22 } 23 return String(stack.reversed()) 24 } 25 }
52ms
1 class Solution { 2 func removeKdigits(_ num: String, _ k: Int) -> String { 3 guard num.count > 0 && k > 0 else { 4 return num 5 } 6 var num = num.map{ String($0) } 7 var stack = [String]() 8 var k = k 9 var i = 0 10 while i < num.count { 11 while stack.count > 0 && num[i] < stack.last! && k > 0 { 12 stack.removeLast() 13 k -= 1 14 } 15 stack.append(num[i]) 16 i += 1 17 } 18 while k > 0 && stack.count > 0 { 19 stack.removeLast() 20 k -= 1 21 } 22 var j = 0 23 while j < stack.count && stack[j] == "0" { 24 j += 1 25 } 26 let result = Array(stack[j..<stack.count]).joined() 27 return result.count == 0 || k > 0 ? "0" : result 28 } 29 }
60ms
1 class Solution { 2 func removeKdigits(_ num: String, _ k: Int) -> String { 3 if num.count == k { return "0" } 4 var array = [Character](num) 5 var stack = [Character]() 6 var count = k 7 for c in array { 8 while stack.count > 0 && stack.last! > c && count > 0 { 9 stack.removeLast() 10 count -= 1 11 } 12 stack.append(c) 13 } 14 while count > 0 { 15 stack.removeLast() 16 count -= 1 17 } 18 19 while stack.count > 0 && stack.first! == "0" { 20 stack.removeFirst() 21 } 22 if stack.count == 0 { 23 return "0" 24 } else { 25 return String(stack) 26 } 27 } 28 }
84ms
1 class Solution { 2 func removeKdigits(_ num: String, _ k: Int) -> String { 3 4 if num.isEmpty || num.count <= k { 5 return "0" 6 } 7 8 var chars = Array(num) 9 // var stack = Array(chars[0 ..< chars.count]) 10 var k = k 11 12 while k > 0 { 13 var idx = 0 14 while idx+1 < chars.count && charToInt(chars[idx]) <= charToInt(chars[idx+1]) { 15 idx += 1 16 } 17 18 if idx == chars.count-1 { 19 chars.removeLast() 20 } else { 21 chars.remove(at:idx) 22 } 23 24 while chars.count > 0 && chars[0] == "0" { 25 chars.removeFirst() 26 } 27 28 if chars.count == 0 { 29 return "0" 30 } 31 32 k -= 1 33 } 34 35 return String(chars) 36 } 37 38 func charToInt(_ char:Character) -> Int { 39 return Int(String(char))! 40 } 41 }
100ms
1 class Solution { 2 func removeKdigits(_ num: String, _ k: Int) -> String { 3 guard num.count > k else{ 4 return "0" 5 } 6 7 var stack : [Int] = [] 8 var k = k 9 for char in num{ 10 while k > 0 && !stack.isEmpty && stack.last! > int(of: char){ 11 stack.removeLast() 12 k -= 1 13 } 14 if int(of: char) == 0 { 15 if !stack.isEmpty{ 16 stack.append(int(of: char)) 17 } 18 }else{ 19 stack.append(int(of: char)) 20 } 21 } 22 23 // there is a possibility in here that K is still greater than 1 24 var result = "" 25 for index in 0..<stack.count-k{ 26 result.append("\(stack[index])") 27 } 28 29 return result.count == 0 ? "0" : result 30 } 31 32 func int(of char : Character)->Int{ 33 return Int(String(char))! 34 } 35 }