8. 字符串转换整数 (atoi) - 力扣（LeetCode） (opens new window)

class Solution {
    public int myAtoi(String s) {
        if (s == null || s.isEmpty()) return 0;
        int index = 0, sign = 1;
        long num = 0;
        // 1. 跳过前导空格
        while (index < s.length() && s.charAt(index) == ' ') index++;
        if (index == s.length()) return 0;
        // 2. 处理符号
        if (s.charAt(index) == '+' || s.charAt(index) == '-') {
            sign = (s.charAt(index) == '-') ? -1 : 1;
            index++;
        }
        // 3. 转换数字
        while (index < s.length() && Character.isDigit(s.charAt(index))) {
            int digit = s.charAt(index) - '0';
            num = num * 10 + digit;
            // 4. 溢出检查
            if (num * sign > Integer.MAX_VALUE) return Integer.MAX_VALUE;
            if (num * sign < Integer.MIN_VALUE) return Integer.MIN_VALUE;
            index++;
        }
        return (int)num * sign;
    }
}

54. 螺旋矩阵 - 力扣（LeetCode） (opens new window)

class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
        if (matrix.length == 0)
            return new ArrayList<Integer>();
        int top = 0;
        int bottom = matrix.length - 1;
        int left = 0;
        int right = matrix[0].length - 1;
        int x = 0;

        // 结果数组大小计算保持不变
        Integer[] res = new Integer[(right + 1) * (bottom + 1)];

        while (true) {
          // 1. 从左向右遍历顶行
           for (int i = left; i <= right; i++) {
                res[x++] = matrix[top][i];
           }  
           if (++top > bottom) break;
           // 2. 从上向下遍历右列
           for(int i = top; i <= bottom; i++) {
                res[x++] = matrix[i][right];
           }
           if (--right < left) break;
           // 3. 从右向左遍历底行
           for (int i = right; i >= left; i--) {
                res[x++] = matrix[bottom][i];
           }
           if (--bottom < top) break;
           // 4. 从下向上遍历左列
           for (int i = bottom; i >= top; i--) {
                res[x++] = matrix[i][left];
           }
           if (++left > right) break;
        }
        return Arrays.asList(res);
    }
}