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;
     }
 }