hdu 1503 LCS

经典的LCS问题。

花了一点点时间完全弄明白了！

开心！DP！我再也不怕你了！

立一个flag：寒假的时候会把所有类型的题目分别写总结。把不会的人教明白了，自己才算真正的明白。

AC代码如下：

#include
#include
using namespace std;

#define N 102

char a[N], b[N];
int dp[N][N],mark[N][N];

void LCS(int al, int bl){
	int i, j;
	for (i = 0; i <= al; i++){
		dp[i][0] = 0;
		mark[i][0] = 1;
	}
	for (i = 0; i <= bl; i++){
		dp[0][i] = 0;
		mark[0][i] = -1;
	}
	for (i = 1; i <= al; i++){
		for (j = 1; j <= bl; j++){
			if (a[i - 1] == b[j - 1]){
				dp[i][j] = dp[i - 1][j - 1]+1;
				mark[i][j] = 0;
			}
			else if (dp[i - 1][j] > dp[i][j - 1]){
				dp[i][j] = dp[i - 1][j];
				mark[i][j] = 1;
			}
			else{
				dp[i][j] = dp[i][j - 1];
				mark[i][j] = -1;
			}
		}
	}
}

void printLCS(int i,int j){
	if (i == 0 && j == 0){
		return;
	}
	if (mark[i][j] == 0){
		printLCS(i - 1, j - 1);
		cout << a[i - 1];
	}
	else if (mark[i][j] == 1){
		printLCS(i - 1, j);
		cout << a[i - 1];
	}
	else if (mark[i][j] == -1){
		printLCS(i, j - 1);
		cout << b[j - 1];
	}
}

int main(){
//	freopen("TestDate.txt", "r", stdin);
	int i,alength,blength;
	while (cin >> a >> b){
		for (i = 0; a[i] != '\0'; i++);
		alength = i;
		for (i = 0; b[i] != '\0'; i++);
		blength = i;
		LCS(alength, blength);
		printLCS(alength, blength);
		cout << endl;
	}
	return 0;
}