Sum 100

Cho chuỗi "123456789", chèn '+', '-' vào giữa chuỗi đó để ra được kết quả 100

 const recursiveFn = (remainNumberList, remainSum = 100, builtStr) => {

    const completed = !remainNumberList && remainSum === 0;
    if (completed && !builtStr.startsWith('*') && !builtStr.startsWith('/') ) {
        console.log(`${builtStr} = ${eval(builtStr)}`);
        return;
    }
    
    const len = remainNumberList.length;
    
    for(let i = 1; i <= len; i++) {
        const prefix = remainNumberList.substr(0, i);
        const postfix = remainNumberList.substr(i, len);
        
        const number = parseInt(prefix);
        
        recursiveFn(postfix, remainSum - number, builtStr + '+' + number);
        recursiveFn(postfix, remainSum + number, builtStr + '-' + number);
    }
}

recursiveFn('123456789', 100, '');