LeetCode: Next Greater Element I

stack和map用好就行

public class Solution {
    public int[] nextGreaterElement(int[] findNums, int[] nums) {
        Stack maxNumSeq = new Stack();
        Map<Integer, Integer> greaterNum = new HashMap<Integer, Integer>();
        for (int i = nums.length-1; i >= 0; i--) {
            while (maxNumSeq.empty() != true) {
                int num = (int)maxNumSeq.peek();
                if (nums[i] < num) {
                    greaterNum.put(nums[i], num);
                    maxNumSeq.push(nums[i]);
                    break;
                }
                else maxNumSeq.pop();
            }
            if (maxNumSeq.empty() == true) {
                maxNumSeq.push(nums[i]);
                greaterNum.put(nums[i], -1);
            }
        }
        int[] ans = new int[findNums.length];
        for (int i = 0; i < ans.length; i++) {
            ans[i] = greaterNum.get(findNums[i]);
        }
        return ans;
    }
}