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LC: string conversion integer (ATOI) + appearance sequence + longest common prefix

2022-07-07 19:30:00 【MyDreamingCode】

1. Please come to realize a  myAtoi(string s)  function , Enable it to convert a string to a 32 Bit signed integer （ similar C/C++ Medium atoi function ）.

function  myAtoi(string s) The algorithm is as follows ：

Read in strings and discard useless leading spaces
Check the next character （ Suppose you haven't reached the end of the character yet ） Positive or negative , Read the character （ If there is ）. Determine whether the final result is negative or positive . If neither exists , Suppose the result is positive .
Read in the next character , Until you reach the next non numeric character or the end of the input . The rest of the string will be ignored .
Convert the numbers read in the previous steps into integers （ namely ,"123" -> 123, "0032" -> 32）. If you don't read in the numbers , Then the integer is 0 . Change the symbol if necessary （ From step 2 Start ）.
If the number of integers exceeds 32 Bit signed integer range [−231,  231 − 1] , You need to truncate this integer , Keep it in this range . say concretely , Less than −231 The integer of should be fixed to −231 , Greater than 231 − 1 The integer of should be fixed to 231 − 1 .
Returns an integer as the final result .

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        var s = "-91283472332";
        var myAtoi = function(s) {
            s = s.trim();
            var sign = 1;
            var index = 0;
            if(s.length<0) return 0 ;
            if(s[index]==='+' || s[index]==='-'){
                if(s[index]==='-')
                    sign = -1;
                index++;
            }
            var res = 0;
            while(index<s.length){
                if(s.charCodeAt(index)-'0'.charCodeAt(0)<0||s.charCodeAt(index)-'0'.charCodeAt(0)>9)
                    break;
                else{
                    res = Number(res * 10) + Number(s[index]);
                }
                index++;
            }
            if((res>(Math.pow(2,31) - 1))&&sign>0)
                return Math.pow(2,31) - 1;
            if((res>Math.pow(2,31))&&sign<0)
                return -Math.pow(2,31);
            return res * sign;
        };
        console.log(myAtoi(s)); //-2147483648
    </script>
</body>
</html>

2.  Given a positive integer n , Output the first... Of the appearance sequence n term .

「 Look-and-say sequence 」 It's a sequence of integers , From numbers 1 Start , Each item in the sequence is a description of the previous one .

You can think of it as a sequence of numeric strings defined by a recursive formula ：

1. 1

2. 11

3. 21

4. 1211

5. 111221

6. 312211

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        var countAndSay = function(n) {
            if(n==1) return '1';
            var s = countAndSay(n-1);
            var num = 0;
            var str = '';
            var count = 0;
            var flag = 0;
            for(var i=0;i<s.length;i++){
                if(s[i]==s[num]){
                    count++;
                    flag = 0;
                }
                else{
                    flag = 1;
                    str += count + s[num];
                    num = i;
                    i = num - 1;
                    count = 0;
                }
            }
            if(!flag)
                str+= count + s[num];
            return str;
        }
        console.log(countAndSay(6)); //312211
    </script>
</body>
</html>

3. Write a function to find the longest common prefix in the string array .

If no common prefix exists , Returns an empty string  "".

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        strs = ["flower","flow","flight"]; 
        var longestCommonPrefix = function(strs) {
            var pre = strs[0];
            var i = 1;
            while(i<strs.length) {
                while(strs[i].indexOf(pre)!=0)
                    pre = pre.slice(0,pre.length-1);
                i++;
            }
            return pre; //fl
        };
    </script>
</body>
</html>

 

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本文为[MyDreamingCode]所创，转载请带上原文链接，感谢
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