Solution 29: 合法的pop序列

public class ValidPopSequence {
public boolean isValidPopSeq(int[] push, int[] pop) {
if (push == null && pop == null) {
return true;
}

int i = 0, j = 0;
Stack<Integer> s = new Stack<Integer>();

while (j < pop.length) {
while (i < push.length) {
if (push[i] != pop[j]) {
s.push(push[i]);
++i;
} else {
// same, no push, pop next
++i;
++j;
break;
}
}
if (i == push.length) {
// end push
// check top of stack with pop
if (s.isEmpty() || s.peek() != pop[j]) {
return false;
}
s.pop();
++j;
}
}

return true;
}
}