[Swift]LeetCode926. 将字符串翻转到单调递增 | Flip String to Monotone Increasing

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A string of '0's and '1's is monotone increasing if it consists of some number of '0's (possibly 0), followed by some number of '1's (also possibly 0.)

We are given a string S of '0's and '1's, and we may flip any '0' to a '1' or a '1' to a '0'.

Return the minimum number of flips to make S monotone increasing.

 Example 1:

Input: "00110"
Output: 1
Explanation: We flip the last digit to get 00111.

Example 2:

Input: "010110"
Output: 2
Explanation: We flip to get 011111, or alternatively 000111.

Example 3:

Input: "00011000"
Output: 2
Explanation: We flip to get 00000000.

 Note:

1. 1 <= S.length <= 20000
2. S only consists of '0' and '1' characters.

---

如果一个由 '0' 和 '1' 组成的字符串，是以一些 '0'（可能没有 '0'）后面跟着一些 '1'（也可能没有 '1'）的形式组成的，那么该字符串是单调递增的。

我们给出一个由字符 '0' 和 '1' 组成的字符串 S，我们可以将任何 '0' 翻转为 '1' 或者将 '1' 翻转为 '0'。

返回使 S 单调递增的最小翻转次数。

 示例 1：

输入："00110"
输出：1
解释：我们翻转最后一位得到 00111.

示例 2：

输入："010110"
输出：2
解释：我们翻转得到 011111，或者是 000111。

示例 3：

输入："00011000"
输出：2
解释：我们翻转得到 00000000。

 提示：

1. 1 <= S.length <= 20000
2. S 中只包含字符 '0' 和 '1'

---

 36ms

class Solution {
    func minFlipsMonoIncr(_ S: String) -> Int {
        var zeros = 0;
        var ones = 0;
        var res = 0;
        var S = Array(S)
        for i in S {
            if i == "0" {
                zeros+=1
            } else {
                ones+=1
            }
        }
        
        var start = 0;
        var end = S.count - 1;
        while end > start {
            if ones >= zeros {
                if(S[end] == "1") {
                    ones-=1
                }
                if S[end] == "0" {
                    zeros-=1
                    res+=1
                }
                end-=1
            }
            else{
                if(S[start] == "0") {
                    zeros-=1
                }
                if(S[start] == "1"){
                    ones-=1;
                    res+=1;
                }
                start+=1;
            }
        }
        return res;    
    }
}

---

56ms

class Solution {
    func minFlipsMonoIncr(_ S: String) -> Int {
        
        var chars = Array(S)
        let totalItems = chars.count
        var prefixSums = [Int](repeating: 0, count: totalItems + 1)
        for i in 0..<chars.count {
            prefixSums[i + 1] = prefixSums[i] + (chars[i] == "1" ? 1 : 0)
        }
        var result = Int.max
        for i in 0..<prefixSums.count {
            
            let flipCounter = prefixSums[i] + (totalItems - i) - (prefixSums.last! - prefixSums[i])
            result = min(result, flipCounter)
        }
        return result
    }
}

---

60ms

class Solution {
    func minFlipsMonoIncr(_ S: String) -> Int {
        var s: [Int] = S.map { $0 == "0" ? 0 : 1}
        var onlyOnes: [Int] = Array(repeating: 0, count: s.count)
        var onlyZeros: [Int] = Array(repeating: 0, count: s.count)
        
        for i in (0..<s.count).reversed() {            
            let prev = (i < (s.count - 1)) ? onlyOnes[i+1] : 0
            onlyOnes[i] = (s[i] == 0 ? 1 : 0) + prev
        }
        
        for i in 0..<s.count {
            let prev = (i > 0) ? onlyZeros[i-1] : 0
            onlyZeros[i] = (s[i] == 1 ? 1 : 0) + prev
        }
        
        var minFlips = min(onlyZeros.last!, onlyOnes.first!)
        for i in 0..<(onlyOnes.count - 1) {
            minFlips = min(minFlips, onlyZeros[i] + onlyOnes[i+1])
        }
        return minFlips
    }    
}

---

108ms

class Solution {
    func minFlipsMonoIncr(_ S: String) -> Int {
        var arr:[Character] = [Character]()
        for char in S.characters
        {
            arr.append(char)
        }       
        let len = S.count
        //声明数组
        var ct:[Int] = [Int](repeating: 0,count: len + 1)
        var x:Int = 0
        for i in 0...len
        {
            ct[i] += x
            if i < len && arr[i] == "1"
            {
                x += 1
            }
        }
        x = 0
        for i in (0...len).reversed()
        {
           ct[i] += x
            if i > 0 && arr[i - 1] == "0"
            {
                x += 1
            }            
        }
        var res = 999999999
        for i in 0...len
        {
            res = min(res,ct[i])
        }
        return res       
    }
}

---

116ms

class Solution {
    func minFlipsMonoIncr(_ S: String) -> Int {
        var arr:[Character] = [Character]()
        for char in S.characters
        {
            arr.append(char)
        }       
        let len = S.count
        //声明数组
        var ct:[Int] = [Int](repeating: 0,count: len + 1)
        var x:Int = 0
        for i in 0...len
        {
            ct[i] += x
            if i < len && arr[i] == "1"
            {
                x += 1
            }
        }
        x = 0
        for i in (0...len).reversed()
        {
           ct[i] += x
            if i > 0 && arr[i - 1] == "0"
            {
                x += 1
            }            
        }
        var res = 999999999
        for i in 0...len
        {
            res = min(res,ct[i])
        }
        return res       
    }
}