求最大子序列

#include <iostream>#include <vector>using namespace std;int max3( int a, int b, int c ){return a > b ? a > c ? a : c : b > c ? b : c;}/** 分治法求最大子序列 * Recursive maximum contiguous subsequence sum algorithm. * Finds maximum sum in subarray spanning a[left..right]. * Does not attempt to maintain actual best sequence. */int maxSumRec( const vector<int> & a, int left, int right ){ if ( left == right ) // Base case if ( a[ left ] > 0 ) return a[ left ]; else return 0; int center = ( left + right ) / 2; int maxLeftSum = maxSumRec( a, left, center ); int maxRightSum = maxSumRec( a, center + 1, right ); int maxLeftBorderSum = 0, leftBorderSum = 0; for ( int i = center; i >= left; i-- ) { leftBorderSum += a[ i ]; if ( leftBorderSum > maxLeftBorderSum ) maxLeftBorderSum = leftBorderSum; } int maxRightBorderSum = 0, rightBorderSum = 0; for ( int j = center + 1; j <= right; j++ ) { rightBorderSum += a[ j ]; if ( rightBorderSum > maxRightBorderSum ) maxRightBorderSum = rightBorderSum; } return max3( maxLeftSum, maxRightSum, maxLeftBorderSum + maxRightBorderSum );}/** * Driver for divide-and-conquer maximum contiguous * subsequence sum algorithm. */int maxSubSum3( const vector<int> & a ){ return maxSumRec( a, 0, a.size( ) - 1 );}/** * Linear-time maximum contiguous subsequence sum algorithm. */int maxSubSum4( const vector<int> & a ){ int maxSum = 0, thisSum = 0; for ( int j = 0; j < a.size( ); j++ ) { thisSum += a[ j ]; if ( thisSum > maxSum ) maxSum = thisSum; else if ( thisSum < 0 ) thisSum = 0; } return maxSum;}/*最大正子序列 所有的sub 都为正数*/int maxSubPositiveSum( const vector<int> & a){ int maxSum = 0, thisSum = 0,i; bool isPositive[8]; for (i = 0 ;i < 8 ; i ++) isPositive[i] = a[i]>0?true:false; for ( int j = 0; j < a.size( ); j++ ) { if ( isPositive[j]) { thisSum += a[ j ]; if ( thisSum > maxSum ) maxSum = thisSum; else if ( thisSum < 0 ) thisSum = 0; } else if (!isPositive[j] ) thisSum = 0; } return maxSum;}int main( ){ vector<int> a( 8 ); a[ 0 ] = 4;a[ 1 ] = -3;a[ 2 ] = 5;a[ 3 ] = -2; a[ 4 ] = -1;a[ 5 ] = 2;a[ 6 ] = 6;a[ 7 ] = -2; int maxSum,i; maxSum = maxSubSum3( a ); cout << "Max sum is " << maxSum << endl; maxSum = maxSubPositiveSum( a ); cout << "Max sum is " << maxSum << endl; return 0;}