Leetcode 03: t58. Length of the last word (simple); Sword finger offer 05. replace spaces (simple); Sword finger offer 58 - ii Rotate string left (simple)

T7: 58. Length of last word （ Simple ）

Give you a string s, It consists of several words , Separate words with spaces . Returns the length of the last word in a string . If there is no last word , Please return 0 .

word It's just letters 、 The largest substring that does not contain any space characters .

Example 1：

 Input ：s = "Hello World"
 Output ：5

Example 2：

 Input ：s = " "
 Output ：0

Tips ：

1 <= s.length <= 104
s Only English letters and spaces ’ ’ form

source ： Power button （LeetCode）
link ：https://leetcode-cn.com/problems/length-of-last-word
Copyright belongs to the network . For commercial reprint, please contact the official authority , Non-commercial reprint please indicate the source .

Ideas

Double pointer upside down , Note that there are spaces at the end , s = " " The situation of , s = "a" The situation of

solution : Double pointer

class Solution {
    
    public int lengthOfLastWord(String s) {
    
        int right = s.length()-1;
        while(right>=0&&s.charAt(right)==' ') right--;
        if(right<0) return 0;
        int left = right;
        while(left>=0&&s.charAt(left)!=' ') left--;
        return right - left;
    }
}

Execution time ：0 ms, In all Java Defeated in submission **100.00%** Users of

Memory consumption ：36.4 MB, In all Java Defeated in submission **95.74%** Users of

On, O1

T8: The finger of the sword Offer 05. Replace blank space （ Simple ）

Please implement a function , Put the string s Replace each space in with "%20".

Example 1：

 Input ：s = "We are happy."
 Output ："We%20are%20happy."

Limit ：

0 <= s The length of <= 10000

Ideas

direct replace

solution : replace

class Solution {
    
    public String replaceSpace(String s) {
    
        return s.replace(" ", "%20");
    }
}

Execution time ：0 ms, In all Java Defeated in submission **100.00%** Users of

Memory consumption ：36.3 MB, In all Java Defeated in submission **62.78%** Users of

On, O1

T9: The finger of the sword Offer 58 - II. Left rotation string （ Simple ）

The left rotation operation of string is to transfer several characters in front of string to the end of string . Please define a function to implement the left rotation operation of string . such as , Input string "abcdefg" And number 2, This function will return the result of rotating two bits to the left "cdefgab".

Example 1：

 Input : s = "abcdefg", k = 2
 Output : "cdefgab"

Example 2：

 Input : s = "lrloseumgh", k = 6
 Output : "umghlrlose"

Limit ：

1 <= k < s.length <= 10000

source ： Power button （LeetCode）
link ：https://leetcode-cn.com/problems/zuo-xuan-zhuan-zi-fu-chuan-lcof
Copyright belongs to the network . For commercial reprint, please contact the official authority , Non-commercial reprint please indicate the source .

Ideas

Use substring()

solution : substring

class Solution {
    
    public String reverseLeftWords(String s, int n) {
    
        return s.substring(n,s.length())+s.substring(0,n);
    }
}

Execution time ：0 ms, In all Java Defeated in submission **100.00%** Users of

Memory consumption ：38.1 MB, In all Java Defeated in submission **87.75%** Users of

On, On