[Golang][Leetcode][String]刷題系列-151-Reverse Words in a String

Steven included in Leetcode Golang

2021-08-09 393 words 2 minutes

Contents

151. Reverse Words in a String

Level : Medium

原題連結 : Click

題目 :

Given an input string s, reverse the order of the words.

A word is defined as a sequence of non-space characters. The words in s will be separated by at least one space.

Return a string of the words in reverse order concatenated by a single space.

Note that s may contain leading or trailing spaces or multiple spaces between two words. The returned string should only have a single space separating the words. Do not include any extra spaces.

Example :

Note

Input: s = “the sky is blue”

Output: “blue is sky the”

Input: s = " hello world "

Output: “world hello”

Input: s = “a good example”

Output: “example good a”

Input: s = " Bob Loves Alice "

Output: “Alice Loves Bob”

Input: s = “Alice does not even like bob”

Output: “bob like even not does Alice”

解題思路 :

這題剛好把一些string的操作都包含進去了
1. 刪除多餘的空白
2. 翻轉字串
3. 翻轉單詞

刪除多餘的空白可以使用two pointers，首先將一個pointer fast放到一次出現字母出現的位置，再來將另一個pointer slow放在起點的位置，然後開始將fast的值搬到slow，開始同步往後走清除頭部的多餘空白，做一些條件控管，讓連續出現的空白才略過，單一個就繼續複製，可以達到每一個單詞之間留有一個空白的效果及刪除掉單詞之間多餘的空白，最後再取slice到最後單詞出現的地方，就可以刪除到尾端的空白
再來翻轉整個字串
最後再執行一些條件控制，讓單詞一個一個翻轉回來就會得到所要的答案

以下是我的解法 - time complexity: O(n) , space complexity: O(1)

Runtime: 0 ms, faster than 100.00% of Go online submissions for Reverse Words in a String.

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func reverseWords(s string) string {
    
    arr := []byte(s)
    fastIndex, slowIndex := 0, 0
    
    // 1. 刪除多餘空白
    for arr[fastIndex] == ' ' {
        fastIndex++
    }
    
    for ;fastIndex < len(arr); fastIndex++ {
        if fastIndex > 0 && arr[fastIndex] == ' ' && arr[fastIndex-1] == arr[fastIndex] {
            continue
        }
        arr[slowIndex] = arr[fastIndex]
        slowIndex++
    }
    
    if slowIndex > 0 && arr[slowIndex-1] == ' ' {
        arr = arr[:slowIndex-1]
    }else {
        arr = arr[:slowIndex]
    }
    
    // 2. 反轉整個字串   
    reverse(&arr, 0, len(arr)-1)
    
    // 3. 反轉所有單詞
    i := 0
    for i < len(arr) {
        j := i
        for ; i < len(arr) && arr[i] != ' ' ; i++ {

        }
        reverse(&arr, j, i-1)
        i++
        

    }
    
    return string(arr)
}


func reverse(arr *[]byte, start int, end int) {
    for start < end {
        (*arr)[start], (*arr)[end] = (*arr)[end], (*arr)[start]
        start++
        end--
    }
}

最後祝福努力認真的各位 “All your dream of are hidden in your daily life” 我們峰頂見!!!