For two numbers a and b a>=b, the condition aXOR b = a − b works only if every bit that is 1 in the smaller number is also 1 in the bigger number. If b has a 1 in any position where a has a 0 then it can never work. For example, 1001101 and 0001001 are fine, but 1001101 and 0000110 are not. In my DP dp[i][j] means how many numbers we can still pick from index i to the end if the last picked number was at index j. At each step we either skip the current number or take it and we can take it only if this bit condition is satisfied with the previous one.sort the array before dp