求最大子序列的原理为什么它能工作?int MaxSubSequenceSum( const int A[],int N){int ThisSum,MaxSum,j;MaxSum = 0;for( j = 0; j < N; j++){ThisSum += A[j];if(ThisSum > MaxSum)MaxSum = ThisSum;else if(ThisSum < 0)ThisSum = 0;}return ThisSum;