1.不开辟空间 倒序数组
int i = 0;
for(int j = 0; j < arr.count; j++) {
long s = arr.count-1-j;
NSObject *str = arr[i];
NSObject *str1 = arr[s];
if (i == s || s-i < 1)break;
arr[i] = str1;
arr[s] = str;
i++;
}
2.round, roundf, roundl, lround, lroundf, lroundl, llround, llroundf, llroundl
round(+2.3) = +2.0 round(+2.5) = +3.0 round(+2.7) = +3.0
round(-2.3) = -2.0 round(-2.5) = -3.0 round(-2.7) = -3.0
round(-0.0) = -0.0
round(-Inf) = -inf
lround(+2.3) = 2 lround(+2.5) = 3 lround(+2.7) = 3
lround(-2.3) = -2 lround(-2.5) = -3 lround(-2.7) = -3
lround(-0.0) = 0
lround(-Inf) = -9223372036854775808
lround(LONG_MAX+1.5) = -9223372036854775808
