这道题放在 DFS 里不太合适，我刚开始就想到了 DP 却没写，DFS 超时后看了题解才发现就是记忆化搜索（白书认为记忆化就是DP）；
1TLE 2WA，把 lens 写成了 lent 后来才发现的。
View Code
# include <cstdio> # include <cstring> # define N 200 + 10 bool finished, f[N][N]; int lens, lent; char s[N], t[N], g[2 * N]; void dfs(int p, int q, int cnt) { if (finished) return; if (cnt == lens+lent) {finished = true; return ;} if (f[p][q]) return ; if (p<lens && s[p] == g[cnt]) dfs(p+1, q, cnt+1); if (q<lent && t[q] == g[cnt]) dfs(p, q+1, cnt+1); f[p][q] = true; } int main() { int T; scanf("%d", &T); for (int i = 1; i <= T; ++i) { scanf("%s%s%s", s, t, g); lens = strlen(s), lent = strlen(t); memset(f, false, sizeof(f)); printf("Data set %d: ", i); finished = false; dfs(0, 0, 0); puts(finished ? "yes":"no"); } return 0; }
Problem Description
Given three strings, you are to determine whether the third string can be formed by combining the characters in the first two strings. The first two strings can be mixed arbitrarily, but each must stay in its original order.
For example, consider forming "tcraete" from "cat" and "tree":
String A: cat
String B: tree
String C: tcraete
As you can see, we can form the third string by alternating characters from the two strings. As a second example, consider forming "catrtee" from "cat" and "tree":
String A: cat
String B: tree
String C: catrtee
Finally, notice that it is impossible to form "cttaree" from "cat" and "tree".
For example, consider forming "tcraete" from "cat" and "tree":
String A: cat
String B: tree
String C: tcraete
As you can see, we can form the third string by alternating characters from the two strings. As a second example, consider forming "catrtee" from "cat" and "tree":
String A: cat
String B: tree
String C: catrtee
Finally, notice that it is impossible to form "cttaree" from "cat" and "tree".
Input
The first line of input contains a single positive integer from 1
through 1000. It represents the number of data sets to follow. The
processing for each data set is identical. The data sets appear on the
following lines, one data set per line.
For each data set, the line of input consists of three strings, separated by a single space. All strings are composed of upper and lower case letters only. The length of the third string is always the sum of the lengths of the first two strings. The first two strings will have lengths between 1 and 200 characters, inclusive.
For each data set, the line of input consists of three strings, separated by a single space. All strings are composed of upper and lower case letters only. The length of the third string is always the sum of the lengths of the first two strings. The first two strings will have lengths between 1 and 200 characters, inclusive.
Output
For each data set, print:
Data set n: yes
if the third string can be formed from the first two, or
Data set n: no
if it cannot. Of course n should be replaced by the data set number. See the sample output below for an example.
Data set n: yes
if the third string can be formed from the first two, or
Data set n: no
if it cannot. Of course n should be replaced by the data set number. See the sample output below for an example.
Sample Input
3 cat tree tcraete cat tree catrtee cat tree cttaree
Sample Output
Data set 1: yes Data set 2: yes Data set 3: no