Use StringBuilder to solve
Intuition\n Describe your first thoughts on how to solve this problem. \n\n# Approach\n Describe your approach to solving the problem. \n\n# Complexity\n- Time 
# Intuition\n<!-- Describe your first thoughts on how to solve this problem. -->\n\n# Approach\n<!-- Describe your approach to solving the problem. -->\n\n# Complexity\n- Time complexity:\n<!-- Add your time complexity here, e.g. $$O(n)$$ -->\n\n- Space complexity:\n<!-- Add your space complexity here, e.g. $$O(n)$$ -->\n\n# Code\n```\nclass Solution {\n    public long findTheArrayConcVal(int[] nums) {\n        long res = 0L;\n        StringBuilder sb = new StringBuilder();\n        int i = 0;\n        int j = nums.length - 1;\n        while(j >= i){\n            if(j == i){\n                sb.append(nums[i]);\n            }else{\n                sb.append(nums[i]).append(nums[j]);\n            }\n            int temp = Integer.parseInt(sb.toString());\n            sb.setLength(0);\n            res += temp;\n            j--;\n            i++;\n        }\n        return res;\n    }\n}\n```
['Java']