Two-pointers Summary

1.单序列

1.1 相向双指针

pair sum: two elements in a sorted array summing to a target

• 167. Two Sum II - Input Array Is Sorted
• 611. Valid Triangle Number  讲解
• 15. 3Sum  讲解
• 16. 3Sum Closest

Palindrome Check

• 1750. Minimum Length of String After Deleting Similar Ends

Reverse OperationsTrapping Water / max volume area: Compute water trapped between heights by moving pointers based on min height.

接雨水类问题，相当于在无序数组中，用双指针在o(n)时间复杂度条件下找到最大值。

• 11. Container With Most Water   讲解

• 42. Trapping Rain Water  讲解

• 633. Sum of Square Numbers

• 658. Find K Closest Elements

1.2 同相双指针

• 611. Valid Triangle Number  讲解

1.3 原地修改

• 27. Remove Element
• 26. Remove Duplicates from Sorted Array
• 80. Remove Duplicates from Sorted Array II
• 75. Sort Colors
• 905. Sort Array By Parity
• 922. Sort Array By Parity II
• 1089. Duplicate Zeros
• 287. Find the Duplicate Number

2.双序列

1.1 双指针

• 2109. Adding Spaces to a String
• 350. Intersection of Two Arrays II

1.2 判断子序列

3.三指针

4.分组循环