算法导论之寻找最大子数组

bool FindMaxmumSubArray(float A[], int low, int high, float &fMaxmumSum, int &iFrom, int &iTo){// 判断输入条件if (low < 0 || high < 0 || low > high){return false;}if (low == high){iFrom = iTo = low;return true;}// 分段;int iMid = (low + high) / 2;// 最大子数组要么在left ~ mid, 或 mid + 1 ~ right, 或横跨mid的 left-right 区间;int iLeftFrom = 0;int iLeftTo = 0;float fLeftSum = 0.0;// 寻找左边数组bool bLeftRes = FindMaxmumSubArray(A, low, iMid, fLeftSum, iLeftFrom, iLeftTo);if (!bLeftRes){return false;}int iRightFrom = 0;int iRightTo = 0;float fRightSum = 0.0;// 寻找右边数组bool bRightRes = FindMaxmumSubArray(A, iMid + 1, high, fRightSum, iRightFrom, iRightTo);if (!bRightRes){return false;}int iCrossingFrom = 0;int iCrossingTo = 0;// 寻找横跨mid 的子数组;float fCrossingSum = 0.0;bool bCrossingRes = FindMaxmumCrossingSubArray(A, low, mid, high, fCrossingSum, iCrossingFrom, iCrossingTo);if (!bCrossingRes){return false;}// 如果左边的子数组和最大if (fLeftSum >= fRightSum && fLeftSum >= fCrossingSum){iFrom = iLeftFrom;iTo = iLeftTo;fMaxmumSum = fLeftSum;} // 如果右边的子数组和最大else if (fRightSum >= fLeftSum && fRightSum >= fCrossingSum){iFrom = iRightFrom;iTo = iRightTo;fMaxmumSum = fRightSum;}else // 最后必定是中间子数组最大;{iFrom = iCrossingFrom;iTo = iCrossingTo;fMaxmumSum = fCrossingSum;}return true;}// 寻找横跨mid的最大子数组;bool FindMaxmumCrossingSubArray(float A[], int low, int mid, int high, float &fCrossingSum, int &iFrom, int &iTo){if (low < 0 || high < 0 || low > high){return false;}float fCurrentSum = 0.0;// 从mid 开始求取左边最大和float fLeftMaxmumSum = -1e7;for (int i=mid; i>=low; i--){fCurrentSum += A[i];if (fCurrentSum > fLeftMaxmumSum){fLeftMaxmumSum = fCurrentSum;iFrom = i;}}// 从mid 开始求取右边最大和fCurrentSum = 0.0;float fRightMaxmumSum = 1e-7;for (int i=mid+1; i<=high; i++){fCurrentSum += A[i];if (fCurrentSum > fRightMaxmumSum){fRightMaxmumSum = fCurrentSum;iTo = i;}}// 最大子数组的和;fCrossingSum = fLeftMaxmumSum + fRightMaxmumSum;return true;}

// by 我执可破. 2016.11.10 于上海浦东;