LC56. 合并区间

class Solution {
    public int[][] merge(int[][] intervals) {
       //先排序
       Arrays.sort(intervals,(v1,v2) -> v1[0] - v2[0]); 
       //创建一个list存放结果
       List<int[]> merged = new ArrayList();
       //判断区间是否重合
        for(int[] interval:intervals){
            //如果列表为空或者没有重复区间那么可以直接加
            //也就是上一个区间的右侧要小于当前区间的左侧
            if(merged.size() == 0 || merged.get(merged.size() - 1)[1] < interval[0]){
                merged.add(interval);
            }else{
                //合并上一个区间,也就是上一个区间的右侧要和当前区间的右侧取一个较大的值
                merged.get(merged.size() - 1)[1] = Math.max(merged.get(merged.size() - 1)[1],interval[1]);
            }
        }
        return merged.toArray(new int[merged.size()][2]);
    }
}

LC69. Sqrt(x)
注：主要是在0 - x 的区间范围当中找一个数的平方小于等于x，考虑二分搜索收缩边界最后返回答案

class Solution {
    public int mySqrt(int x) {
        int ans = 0,left = 0,right = x;
        while(left <= right){
            int mid = left + (right - left) / 2;
            if((long) mid * mid <= x){
                ans = mid;
                left = mid + 1;
            }else{
                right = mid - 1;
            }
        }
        return ans;
    }
}

LC82. 删除排序链表中的重复元素 II

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode deleteDuplicates(ListNode head) {
        ListNode dummy = new ListNode(0,head);
        ListNode cur = dummy;
        while(cur.next != null && cur.next.next != null){
            if(cur.next.val == cur.next.next.val){
                int x = cur.next.val;
                while(cur.next != null && cur.next.val == x){
                    cur.next = cur.next.next;
                }
            }else{
                cur = cur.next;
            }
        }
        return dummy.next;
    }
}