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;
	}
}