[670] Maximum Swap

雖然不知道為什麼覺得要把它倒過來，而且還是字元轉數字，寫完發現不需要啊XD

把自己搞暈之外，還要多做拆開再合起來組成數字，是在自找麻煩嗎 囧

但暫時不想重寫了，先降子XD

void swap(int *a, int *b)

{

int tmp = *a;

*a = *b;

*b = tmp;

}

int maximumSwap(int num) {

int *stack = calloc (9 , sizeof (int));

int top = -1;

int running = num;

while (running >0){

stack[++top] = (running %10);

running /= 10;

}

if (num==0)

stack[++top] =0;

int max=INT_MIN;

int max_idx = 0;

int *rightmax = calloc (top+1 , sizeof (int));

for (int i=0; i<=top;i++){

rightmax[i]= max_idx;

if (stack[i]>max)

{

max = stack[i];

max_idx = i;

rightmax[i]=i;

}

}

for (int i=top; i>=0; i--){

if (stack[i]<stack[rightmax[i]]){

swap(&stack[i],&stack[rightmax[i]]);

break;

}

}

int ret = 0;

while (top >=0)

ret = ret*10+stack[top--];

return ret;

}