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Here are two strings start and target , The length is n . Each string only By the character ‘L’、‘R’ and ‘_’ form , among ：

• character ‘L’ and ‘R’ Represents a fragment , In which the fragment ‘L’ There is only one directly on its left vacancy Only when Left Move , And fragments ‘R’ There is only one directly on its right vacancy Only when Right Move .
• character ‘_’ It means that it can be arbitrarily ‘L’ or ‘R’ The space occupied by the fragment .

If you are moving a string start You can get the string after any number of fragments in target , return true ; otherwise , return false .

Example 1：

 Input ：start = "_L__R__R_", target = "L______RR"
 Output ：true
 explain ： From the string  start  get  target , The following movements are required ：
-  Move the first clip one step to the left , The string now becomes  "L___R__R_" .
-  Move the last clip one step to the right , The string now becomes  "L___R___R" .
-  Move the second clip to the right for a walk , The string now becomes  "L______RR" .
 From the string  start  obtain  target , So back  true .

Example 2：

 Input ：start = "R_L_", target = "__LR"
 Output ：false
 explain ： character string  start  Medium  'R'  The clip can be moved one step to the right to get  "_RL_" .
 however , After this step , There are no moving clips , So you can't get from the string  start  obtain  target .

Example 3：

 Input ：start = "_R", target = "R_"
 Output ：false
 explain ： character string  start  The clip in can only move to the right , So you can't get from the string  start  obtain  target .

Problem solving

Writing a ：

Reference link

class Solution {
    
public:
    bool canChange(string start, string target) {
    
        string s=start,t=target;
        s.erase(remove(s.begin(),s.end(),'_'),s.end());
        t.erase(remove(t.begin(),t.end(),'_'),t.end());
        if(s!=t) return false;
        
        for(int i=0,j=0;i<start.size();i++){
    
            if(start[i]=='_') continue;
            while(j<target.size()&&target[j]=='_') j++;
            if(start[i]=='L'&&i<j) return false;
            if(start[i]=='R'&&i>j) return false;
            j++;
        }
        return true;
        
    }
};