力扣题目方法

1323.valueOf方法的互相转换

258.求树根

//1、递归，注意求所有位数相加和的方法
public int addDigits(int num) {
    if (num < 10) {
        return num;
    }
    int next = 0;
    while (num != 0) {
        next = next + num % 10;
        num /= 10;
    }
    return addDigits(next);
}
//2、数理方法
return (num - 1) % 9 + 1;

496、求下一个比本数大的数

public class Solution {
    public int[] nextGreaterElement(int[] findNums, int[] nums) {
        Stack < Integer > stack = new Stack < > ();
        HashMap < Integer, Integer > map = new HashMap < > ();
        int[] res = new int[findNums.length];
        for (int i = 0; i < nums.length; i++) {
            while (!stack.empty() && nums[i] > stack.peek())
                map.put(stack.pop(), nums[i]);
            stack.push(nums[i]);
        }
        while (!stack.empty())
            map.put(stack.pop(), -1);
        for (int i = 0; i < findNums.length; i++) {
            res[i] = map.get(findNums[i]);
        }
        return res;
    }
}

1189.求数组中特定位数的最小值。