1. 百钱百鸡
   百钱百鸡：公鸡5文钱一只，母鸡3文钱一只，小鸡3只一文钱， 用100文钱买一百只鸡,其中公鸡，母鸡，小鸡都必须要有，问公鸡，母鸡，小鸡要买多少只刚好凑足100文钱？

/*
思路：三元方程，设公鸡，母鸡，鸡仔各为x,y,z
         5x < 100 => x < 20;
         3y < 100 => y < 33
         z = 100 - x - y
*/
for (var x = 1; x < 20; x++) {
        for (var y = 1; y < 33 - x; y++) {
            var z = 100 - x - y;
            // console.log("x = " + x + "y = " + y + "z = " + z);
            if (z % 3 != 0) continue;
            // console.log("z = " + z);
            if (5 * x + 3 * y + z / 3 == 100) {
                console.log("result: x = " + x + " y = " + y + " z = " +  z);
            }
        }
    }
    /*
    result: x = 4 y = 18 z = 78
    result: x = 8 y = 11 z = 81
    result: x = 12 y = 4 z = 84
    */