LeetCode: Next Greater Element I

stack和map用好就行

 1 public class Solution {
 2     public int[] nextGreaterElement(int[] findNums, int[] nums) {
 3         Stack maxNumSeq = new Stack();
 4         Map<Integer, Integer> greaterNum = new HashMap<Integer, Integer>();
 5         for (int i = nums.length-1; i >= 0; i--) {
 6             while (maxNumSeq.empty() != true) {
 7                 int num = (int)maxNumSeq.peek();
 8                 if (nums[i] < num) {
 9                     greaterNum.put(nums[i], num);
10                     maxNumSeq.push(nums[i]);
11                     break;
12                 }
13                 else maxNumSeq.pop();
14             }
15             if (maxNumSeq.empty() == true) {
16                 maxNumSeq.push(nums[i]);
17                 greaterNum.put(nums[i], -1);
18             }
19         }
20         int[] ans = new int[findNums.length];
21         for (int i = 0; i < ans.length; i++) {
22             ans[i] = greaterNum.get(findNums[i]);
23         }
24         return ans;
25     }
26 }