Method findTargetSumWays

java/0494-target-sum.java:6–9

(int[] nums, int S)

    HashMap<String, Integer> dp;
   
    public int findTargetSumWays(int[] nums, int S) {
        dp = new HashMap<>();
        return calculate(nums, 0, 0, S);
    }
    
    public int calculate(int[] nums, int i, int sum, int S) {
        String s = i + "," + sum;