<p>Given a string <code>num</code> that contains only digits and an integer <code>target</code>, return <em><strong>all possibilities</strong> to insert the binary operators </em><code>&#39;+&#39;</code><em>, </em><code>&#39;-&#39;</code><em>, and/or </em><code>&#39;*&#39;</code><em> between the digits of </em><code>num</code><em> so that the resultant expression evaluates to the </em><code>target</code><em> value</em>.</p>

<p>Note that operands in the returned expressions <strong>should not</strong> contain leading zeros.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> num = &quot;123&quot;, target = 6
<strong>Output:</strong> [&quot;1*2*3&quot;,&quot;1+2+3&quot;]
<strong>Explanation:</strong> Both &quot;1*2*3&quot; and &quot;1+2+3&quot; evaluate to 6.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> num = &quot;232&quot;, target = 8
<strong>Output:</strong> [&quot;2*3+2&quot;,&quot;2+3*2&quot;]
<strong>Explanation:</strong> Both &quot;2*3+2&quot; and &quot;2+3*2&quot; evaluate to 8.
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> num = &quot;3456237490&quot;, target = 9191
<strong>Output:</strong> []
<strong>Explanation:</strong> There are no expressions that can be created from &quot;3456237490&quot; to evaluate to 9191.
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= num.length &lt;= 10</code></li>
	<li><code>num</code> consists of only digits.</li>
	<li><code>-2<sup>31</sup> &lt;= target &lt;= 2<sup>31</sup> - 1</code></li>
</ul>

class Solution {
public:
    vector<string> ans;
    vector<string> addOperators(string num, int target) {
        dfs(0,0,0,"",num,target);
        return ans;
    }

    void dfs(int idx,long long pre,long long sum,string path,string num,int target){
        if(idx==num.size()){
            if(sum==target){
                ans.push_back(path);
            }
            return;
        }
        long long curr=0;
        for(int i=idx;i<num.size();i++){
            if(num[idx]=='0'&&i!=idx){
                return;
            }
            curr=curr*10+num[i]-'0';
            if(idx==0){
                dfs(i+1,curr,curr,to_string(curr),num,target);
            }else{
                dfs(i+1,curr,sum+curr,path+"+"+to_string(curr),num,target);
                dfs(i+1,-curr,sum-curr,path+"-"+to_string(curr),num,target);
                dfs(i+1,pre*curr,sum-pre+pre*curr,path+"*"+to_string(curr),num,target);
            }
            
        }
    }
};
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