Delete duplicates in an ordered array ii[double pointers -- unified in multiple cases]

Preface

A lot of algorithms , There is no need to take simulation , The simulation will have a lot of situations , You need a lot if, Even you if Don't come here ,if There is if.
Learn to handle multiple situations in a unified way , Let simple code complete is the right way .

One 、 Remove duplicate items from an ordered array II

Two 、 Double pointer

package everyday.doublePoint;

public class RemoveDuplicates {
    
    /* target: Modify array in place , The number of elements in an ascending array cannot exceed two , namely 1-2 individual . Finally, return the number of valid elements modified previously .  A pointer to the position that can actually be assigned , A pointer traverses nums All the elements , Assign all legal elements to the actual pointer .  Use a variable record to record illegal numbers , use nums.length -  The illegal number is the actual length . */
    public int removeDuplicates(int[] nums) {
    
        //  The position that can actually be assigned .
        int real = 0;
        //  Record who the previous variable is , And how much of this variable has been repeated .
        int pre = 1 << 31, sameNum = 0;
        //  Record the effective length of the array .
        int len = nums.length;
        //  The second pointer traverses nums Array , Filter the number of qualified .
        for (int i = 0; i < nums.length; i++) {
    
            //  Not equal to the front , The new value , Reset required pre/sameNum, And assign the qualified value to real It's about .
            if (pre != nums[i]) {
    
                pre = nums[i];
                sameNum = 1;
                nums[real++] = nums[i];
            }
            //  The same element does not exceed 2
            else if (sameNum++ < 2) nums[real++] = nums[i];
                //  The same element exceeds 2, Invalid elements 
            else --len;
        }
        return len;
    }
}

summary

1） Double pointer
2） Find a uniform way to deal with , It's an algorithm .

reference

[1] LeetCode Remove duplicate items from an ordered array II