Leetcode306累加数（递归解决）

```javascript
/**
 * @param {string} num
 * @return {boolean}
 */
var isAdditiveNumber = function(num) {
    let flag = false
var addStrings = function(num1, num2) {
    let arr1 = num1.split('').map(item=>{return Number(item)})
    let arr2 = num2.split('').map(item=>{return Number(item)})
    let jin = 0
    let str = ''
    while(arr1.length || arr2.length || jin){
        let number1 = arr1.pop() || 0
        let number2 = arr2.pop() || 0
        str =(jin + number2 + number1)%10 + st
        jin = Math.floor((jin + number2 + number1)/10) 
    }
    return st

};
    function dfs(pre,curr,rest){
        if(pre.length >1 && pre[0] === "0"){
            return
        }
        if(curr.length >1 && curr[0] === "0"){
            return
        }
        if(rest === ''){
            flag = true
            return
        }
        let total = addStrings(pre,curr)
        if(rest.length < total.length){
            return
        }
        let next = rest.substring(0,total.length)
        if(next === total){
            dfs(curr,next,rest.substring(total.length))
        }
        
    }

    // i是第一个字符串尾部对应的索引
    // j是第二个字符串尾部对应的索引
    for(let i=0;i<num.length;i++){
        // TODO
        // 进一步，限制
        // 进一步
        // 搞定这个i j的关系
        for(let j=i+1;j-i<=num.length -j;j++){
            if(num.substring(j+1)){
            dfs(num.substring(0,i+1),num.substring(i+1,j+1),num.substring(1+j))
            }
        }
    }
    return flag

};
```