LeetCode No556. 下一个更大元素 III

class Solution {
    public int nextGreaterElement(int n) {
        char[] str = String.valueOf(n).toCharArray();
        int[] arr = new int[str.length];
        for(int i=0; i<str.length; i++) {
            arr[i] = (int)(str[i] - '0');
        }
        nextPermutation(arr);
        long sum = 0;
        for(int i=0; i<str.length; i++) {
            sum = sum * 10 + (long)(arr[i]);
            if( sum > Integer.MAX_VALUE) {
                return -1;
            }
        }
        if( sum <=n ) {
            return -1;
        }
        return (int) sum;
    }

    private void nextPermutation(int[] nums) {
        int len = nums.length;
        boolean flag = false;
        for(int i=len-1; i>0; i--) {
            if( nums[i-1]<nums[i] ) {
                int low = i - 1;
                // System.out.println(low);
                int j = len - 1;
                while( j>=0 && nums[j]<=nums[low] ) {
                    j --;
                }
                swap(nums, j, low);
                reverse(nums, low+1);
                flag = true;
                break;
            }
        }
        if( !flag ) {
            Arrays.sort(nums);
        }
    }
    private void swap(int[] nums, int i, int j) {
        int temp = nums[j];
        nums[j] = nums[i];
        nums[i] = temp;
    }

    private void reverse(int[] nums, int start) {
        int left = start, right = nums.length - 1;
        while (left < right) {
            swap(nums, left, right);
            left++;
            right--;
        }
    }


}