双指针的while循环，从两边到中间遍历。

private static int maxArea(int[] height) {
    int maxArea = 0;
    int i = 0, j = height.length - 1;
    while (i < j && i >= 0 && j <= height.length - 1) {
        maxArea = Math.max(maxArea, Math.min(height[i], height[j]) * (j - i));
        if (height[i] > height[j])
            j--;
        else
            i++;
    }
    return maxArea;
}

private static List
 
  > threeSum(int[] nums) {
        List
  
   > ansList = new ArrayList<>(); if (nums.length < 3) return ansList; Arrays.sort(nums); for (int i = 0; i < nums.length - 2; i++) { if (i == 0 || nums[i - 1] < nums[i]) { int st = i + 1; int en = nums.length - 1; while (st < en) { int sum = nums[i] + nums[st] + nums[en]; if (sum == 0) { ansList.add(Arrays.asList(nums[i], nums[st], nums[en])); st++; en--; while (st < en && nums[st] == nums[st - 1]) st++; while (st < en && nums[en] == nums[en + 1]) en--; } else if (sum > 0) en--; else st++; } } } return ansList; }