//假設有pow函數，Linux下編譯一定要加-lm
//gcc ReverseInteger.c -o ReverseInteger -lm
關鍵：一定要註意操作過程中int類型超界
有可能輸入數據沒有超界。可是反向逆序後，甚至在逆序操作過程中都有可能超界。反正時刻檢查超界與否

#include <stdlib.h>
#include <stdio.h>
#include <math.h>
#include <limits.h>

int reverse(int x) {
    int f = 0;
    int
 
 k = 0;
    int m = 0;
    int tem=0;
    int r = 0;
    int INT_MAX_DIV10 = INT_MAX / 10;
    if(x<-INT_MAX && x >INT_MAX) 
        return 0;

    if(x < 0) 
    {
        x = -x;
        f = 1;
    }
    while(x)
    {   
        if(r > INT_MAX_DIV10) return 0;
        r = r*10;
        tem = x
 
 % 10;
        if(INT_MAX - tem < r) return 0;
        r = r + tem;
        x = x/10;
    }
    if(f)
        r = -r;

    return r;
}

int main()
{
    int x = 1;
    int r = reverse(x);
    printf("reverse x %d = %d \n",x,r);

    x = 13579;
    r = reverse(x);
    printf("reverse x %d = %d \n",x,r);

    x
 
 = 0;
    r = reverse(x);
    printf("reverse x %d = %d \n",x,r);

    x = -13579;
    r = reverse(x);
    printf("reverse x %d = %d \n",x,r);

    x = -1;
    r = reverse(x);
    printf("reverse x %d = %d \n",x,r);

    x = 1534236469; //原數不超界。逆序超界
    r = reverse(x);
    printf("reverse x %d = %d \n",x,r);
}

[Leetcode]-Reverse Integer