[Leetcode] Maximum Subarray

Find the contiguous subarray within an array (containing at least one number) which have the largest sum.

For example, given the array [−2,1,−3,4,−1,2,1,−5,4] ,
The contiguous Subarray has the [4,−1,2,1] largest sum = 6 .

Idea one: The idea of dynamic planning. Time complexity O (n), Spatial complexity O (1). The code of question 31, which is not only a good space-time complexity, but also a better handling of invalid input.

If the argument is a null pointer, the array length is less than 0. This returns 0. For the maximum value of the area molecule array is 0 and invalid input for both of the different requests. Sets a global variable to mark whether the input is invalid.

1 BOOLG_invalidinput =false;2 3 intFindgreatestsumofsubarray (int*pdata,intnlength) {4     if((PData = = NULL) | | (Nlength <=0))5     {6G_invalidinput =true;7         return 0;8     }9 TenG_invalidinput =false; One  A     intNcursum =0; -     intNgreatestsum =0x80000000; -      for(inti =0; i < nlength; ++i) the     { -         if(Ncursum <=0)  -Ncursum =Pdata[i]; -         Else +Ncursum + =Pdata[i]; -  +         if(Ncursum >ngreatestsum) ANgreatestsum =ncursum; at     } -  -     returnngreatestsum; -}

Idea two: Divide and conquer the strategy. Time complexity O (NLGN), Spatial complexity O (1).

1 classSolution {2  Public:3     intMaxsubarray (intA[],intN) {4     returnMaxsubarray (A,0N1);5 }6 7 intMaxsubarray (intA[],intLowintHigh ) {8     if(Low = = high)returnA[low];9 Ten     intMid = (low + high)/2; One     intMax_left_sum =Maxsubarray (A, Low, mid); A     intMax_right_sum = Maxsubarray (A, Mid +1, high); -  -     intMax_cross_leftsum = int_min, cross_leftsum =0; the      for(inti = mid; I >= low; --i) { -Cross_leftsum + =A[i]; -         if(Cross_leftsum >max_cross_leftsum) -Max_cross_leftsum =cross_leftsum; +     } -  +     intMax_cross_rightsum = int_min, cross_rightsum =0; A      for(inti = mid +1; I <= high; ++i) { atCross_rightsum + =A[i]; -         if(Cross_rightsum >max_cross_rightsum) -Max_cross_rightsum =cross_rightsum; -     } -  -     intMax_cross_sum = Max_cross_leftsum +max_cross_rightsum; in  -     if(Max_left_sum >= max_cross_sum && max_left_sum >=max_right_sum) { to         returnmax_left_sum; +}Else if(Max_right_sum >= max_cross_sum && max_right_sum >=max_left_sum) { -         returnmax_right_sum; the}Else { *         returnmax_cross_sum; $     }Panax Notoginseng } -};

[Leetcode] Maximum Subarray