TriangleGenerator.java

public String triangleGenerator(int num, char letter ){
    if(num%2==0){
        num++
    }
//     int num = 21; // input num (assume odd)
//     char letter = 'A'; // input char

    int rows = (num+1)/2; // the amount of rows
    String result = "";
    int rowIdx = 1; // assume the idx of first row is 1

    while (rowIdx<=rows){
        int colIdx = 0;
        // special case for 1st row
        if (rowIdx==1){
            while(colIdx<num){
                // assume the idx of first letter in a row is 0
                if (colIdx==(num-1)/2){
                    result+=letter;
                }else {
                    result+=" ";
                }
                colIdx++;
            }
        }else if (rowIdx==rows){
            // special case for last row
            while (colIdx<num){
                result+=letter;
                colIdx++;
            }
        }else{
            // middle row case
            int idx1 = (num-1)/2-(rowIdx-1);
            int idx2 = (num-1)/2+(rowIdx-1);
            while (colIdx<num){
                if (colIdx==idx1||colIdx==idx2){
                    result+=letter;
                }else {
                    result+=" ";
                }
                colIdx++;
            }
        }
        result+="\n";
        rowIdx++;
    }
    // output result
//     System.out.println(result);
    return result;
}