RangeAddition.java

public int[] rangeAdd(int size, int[][] updates) {
  //Concept question since the idea of sorting/merging is more complicated.
  
  // The logic add all values from start index to "end of array" instead of end index. 
  // But to avoid the additional add, update the end+1 index with negative value(-x).
  // This compensates the +x till the end of array. (+x -x = 0)

//res[0,2,3,0,-5]: <- obtained from the first loop.

//sum[0] = res[0] = 0;

//sum[1] = res[0] + res[1] = 0 + 2 = 2;

//sum[2] = res[0] + res[1] + res[2] = 0 + 2 + 3 = 5;

//sum[3] = res[0] + res[1] + res[2] + res[3] = 0 + 2 + 3 + 0 = 5;

//sum[4] = res[0] + res[1] + res[2] + res[3] + res[4] = 0 + 2 + 3 + 0 + (-5) = 0;

//sum[0,2,5,5,0]
  
  int[] result = new int[size];
  for(int i = 0; i < updates.length; i++) {
   //update result with start values.
    int startIndex = updates[i][0];
    int value = updates[i][2];
    int endIndex = updates[i][1];
    result[startIndex] = value;
    if(endIndex < size-1) result[endIndex+1] = -value;
  }
  
  // adding elemnts from startIndices to end of array instead of end indices
  for(int i = 1; i < size; i++) {
    result[i] = result[i-1] + result[i];  
  }
  return result;
}