[leedcode oj 8]String to Integer (atoi)

Implement atoi to convert a string to an integer.

Hint: Carefully consider all possible input cases. If you want a challenge, please do not see below and ask yourself what are the possible input cases.

Notes: It is intended for this problem to be specified vaguely (ie, no given input specs). You are responsible to gather all the input requirements up front.

字面意思看起来，就是一个善良的atoi，然而我曾经都是暴力的知道几位数。。。嘤嘤。。。

一想到string有length函数啊。。。就写了这货。。然后就。。。恩。。。悲剧了。。。为虾米呢。。。

class Solution {public:    int myAtoi(string str) {        int n = str.length();        int num = 0;        int j = 1;        for(int i = n - 1;i >= 0;i--)        {            num += j * str[i];            j *= 10;        }        return num;    }};

啊。。。你猜string和int乘会是什么。。。会是神奇的东西。。。

开心的写了下面这货。。。然后发现。。。卧槽用例还有正负号啊。。。

class Solution {public:    int myAtoi(string str) {        int n = str.length();        int num = 0;        int j = 1;        for(int i = n - 1;i >= 0;i--)        {            int tmp;            tmp = str[i] - '0';            num += j * tmp;            j *= 10;        }        return num;    }};

为了正负号，我机智的写了这货，然后又submit，蓝后。。。出了个用例“+-2”。。。

class Solution {public:    int myAtoi(string str) {        int n = str.length();        int num = 0,flag = 1,j = 1;        int k = 0;        if(str[0] == '+')        {            k++;        }        if(str[0] == '-')        {            flag = 0;            k++;        }        for(int i = n - 1;i >= k;i--)        {            int tmp;            tmp = str[i] - '0';            num += j * tmp;            j *= 10;        }        if(flag == 0)        {            num = 0 - num;        }        return num;    }};

于是我发现。。。原来有一件事情，叫做预处理

class Solution {public:    int myAtoi(string str) {        int n = str.length();        int positive = 1;        int first = 0;        int error = 0;        string str_tmp;        int num = 0;        int j = 1;        if(str[0] == '+')        {            first = 1;        }        if(str[0] == '-')        {            first = 1;            positive = 0;        }        for(int i = first;i < str.length();i++)        {            if(str[i] <= '9' && str[i] >= '0')            {                str_tmp[i] = str[i];            }            else            {                error = 1;            }        }        for(int i = n - 1;i >= first;i--)        {            int tmp;            tmp = str_tmp[i] - '0';            num += j * tmp;            j *= 10;        }        if(positive == 0)        {            num = 0 - num;        }        if(error == 1)        {            num = 0;        }        return num;    }};

哈哈哈哈。。。然后又没过。。。你猜为什么。。。因为用例出现了。。前面有空格。。。恩。。。

class Solution {public:    int myAtoi(string str) {        int n = str.length();        int positive = 1;        int first = 0;        int error = 0;        string str_tmp;        int num = 0;        int j = 1;        while(str[first] == ' ')        {            first++;        }        if(str[first] == '+')        {            first++;        }        else if(str[first] == '-')        {            first++;            positive = 0;        }        for(int i = first;i < str.length();i++)        {            if(str[i] <= '9' && str[i] >= '0')            {                str_tmp[i] = str[i];            }            else            {                error = 1;            }        }        for(int i = n - 1;i >= first;i--)        {            int tmp;            tmp = str_tmp[i] - '0';            num += j * tmp;            j *= 10;        }        if(positive == 0)        {            num = 0 - num;        }        if(error == 1)        {            num = 0;        }        return num;    }};

哈哈哈哈。。。然后出了一个神用例。。。。" -0012a42"。。。expected-12完全没懂啥意思。。。后来。。。啊。。。好像是有了数之后。。。后面的直接忽略。。。哈哈哈哈。。。

class Solution {public:    int myAtoi(string str) {        int n = str.length();        int positive = 1;        int first = 0;        int error = 0;        string str_tmp;        int num = 0;        int j = 1;        while(str[first] == ' ')        {            first++;        }        if(str[first] == '+')        {            first++;        }        else if(str[first] == '-')        {            first++;            positive = 0;        }        for(int i = first;i < str.length();i++)        {            if(str[i] <= '9' && str[i] >= '0')            {                str_tmp[i] = str[i];            }            else if(i == first)            {                error = 1;            }            else            {                n = i;                break;            }        }        for(int i = n - 1;i >= first;i--)        {            int tmp;            tmp = str_tmp[i] - '0';            num += j * tmp;            j *= 10;        }        if(positive == 0)        {            num = 0 - num;        }        if(error == 1)        {            num = 0;        }        return num;    }};

然后神用例又出现了。。。越界问题。。。崩溃边缘

Input:"2147483648"

Output:-2147483648

Expected:2147483647

class Solution {public:    int myAtoi(string str) {        int n = str.length();        int positive = 1;        int first = 0;        int error = 0;        string str_tmp;        long num = 0;        int j = 1;        while(str[first] == ' ')        {            first++;        }        if(str[first] == '+')        {            first++;        }        else if(str[first] == '-')        {            first++;            positive = 0;        }        for(int i = first;i < str.length();i++)        {            if(str[i] <= '9' && str[i] >= '0')            {                str_tmp[i] = str[i];            }            else if(i == first)            {                error = 1;            }            else            {                n = i;                break;            }        }        for(int i = n - 1;i >= first;i--)        {            int tmp;            tmp = str_tmp[i] - '0';            num += j * tmp;            j *= 10;        }        if(num > 2147483647 && positive == 1)        {            num = 2147483647;        }        if(positive == 0)        {            if(num >= 2147483648)            {                num = 2147483648;            }            num = 0 - num;        }                if(error == 1)        {            num = 0;        }        return num;    }};

哈哈哈。。。又来了神奇的东西。。。

Input:" 10522545459"

Output:1932610867

Expected:2147483647

啊啊啊啊啊啊！！！！什么鬼！！！！！
传说。。这是位数问题。。。红红火火恍恍惚惚

class Solution {public:    int myAtoi(string str) {        int n = str.length();        int positive = 1;        int first = 0;        int error = 0;        string str_tmp;        long num = 0;        int j = 1;        while(str[first] == ' ')        {            first++;        }        if(str[first] == '+')        {            first++;        }        else if(str[first] == '-')        {            first++;            positive = 0;        }        for(int i = first;i < str.length();i++)        {            if(str[i] <= '9' && str[i] >= '0')            {                str_tmp[i] = str[i];            }            else if(i == first)            {                error = 1;            }            else            {                n = i;                break;            }        }        for(int i = n - 1;i >= first;i--)        {            int tmp;            tmp = str_tmp[i] - '0';            num += j * tmp;            j *= 10;        }        if((n - first >=11 || num > 2147483647) && positive == 1)        {            num = 2147483647;        }        if(positive == 0)        {            if(n - first >=11 || num >= 2147483648)            {                num = 2147483648;            }            num = 0 - num;        }        if(error == 1)        {            num = 0;        }        return num;    }};

哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈哈，终于AC了。。。