swap交换2变量
#define swap(x,y) {(x)=(x)+(y); (y)=(x)-(y); (x)=(x)-(y);}
void swap(int i, int offset){ int temp; temp = a[offset]; a[offset] = a[i]; a[i] = temp; }
#define swap(x,y) {(x)=(x)+(y); (y)=(x)-(y); (x)=(x)-(y);}
void swap(int i, int offset){ int temp; temp = a[offset]; a[offset] = a[i]; a[i] = temp; }