如何找到链的最后一个孩子

Question

How to find the last element of this chain given in the code is the array(Symptomaster history array).

I have used recursion. I will show in the code.

//example data in array
0: SymptomasterHistory {parentId: -1, currentId: 798, rootBool: true, hasChild: true}
1: SymptomasterHistory {parentId: -1, currentId: 235, rootBool: true, hasChild: true}
2: SymptomasterHistory {parentId: 798, currentId: 799, rootBool: false, hasChild: false}
3: SymptomasterHistory {parentId: 235, currentId: 237, rootBool: false, hasChild: true}
4: SymptomasterHistory {parentId: 237, currentId: 274, rootBool: false, hasChild: false}

// recursion
findResultByParentId(parentId: number) {
        for (let i = 0; i < this.childSymptomaster.length; i++) {
            if(this.childSymptomaster[i].parentId === parentId && this.childSymptomaster[i].hasChild){
                this.findResultByParentId(this.childSymptomaster[i].currentId);
            }else{
                let id = this.childSymptomaster[i].currentId;
                this.childSymptomaster.splice(i,1);
                return id;
            }
        }
    }

Example of using recursion, parent id is 798 and the result should be 799. Help me, please.

Answer 1

The reason it doesn't work for you is because you have the recursive case inside the loop. In reality you should do this:

function findResultByParentId(id) {
        // Find the current element
        var currentElement = this.childSymptomaster.find(function(e) { 
          return e.currentId === id;
        });
        // If current element id doesn't exist
        if (!currentElement) {
          // Return error value -1, null, undefined or similar
          return -1;
        }

        if (currentElement.hasChild) {
          // Recursive case
          // The element have a child - find it...
          var child = this.childSymptomaster.find(function(c) {
            return c.parentId === id;
          });
          // check for that child
          return findResultByParentId(child.currentId);
        } else {
          // Base case - we are at the bottom leaf
          return currentElement.currentId;
        }
    }

For a more compressed version using arrow functions:

function findResultByParentId(id) {
        // Find the current element
        let currentElement = this.childSymptomaster.find((e) => e.currentId === id);
        // If current element id doesn't exist
        if (!currentElement) {
          // Return error value -1, null, undefined or similar
          return -1;
        }

        if (currentElement.hasChild) {
          // Recursive case
          // The element have a child - find it...
          let child = this.childSymptomaster.find((c) => c.parentId === id);
          // Check for that child
          return findResultByParentId(child.currentId);
        } else {
          // Base case - we are at the bottom leaf
          return currentElement.currentId;
        }
    }

For a working plunker see this: https://plnkr.co/edit/leSUKQCpt5xCnFvSR0ca?p=preview