二维dp
dp[i][j] 表示是否能有s1[0...i-1]和[s2[0....j-1]组成s3【0.....i+j-1】
class Solution {
public:
bool isInterleave(string s1, string s2, string s3) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
int len1 = s1.length();
int len2 = s2.length();
int len3 = s3.length();
if(len1+len2!=len3)
return false;
if(len1==0&&s2!=s3)
return false;
if(len2==0&&s1!=s3)
return false;
bool** dp = new bool *[len1+1];
for(int i =0;i<=len1;i++)
dp[i] = new bool[len2+1];
dp[0][0] = 1;
for(int i =1;i<=len1;i++)
if(dp[i-1][0]&&s1[i-1]==s3[i-1])
dp[i][0] = true;
else
dp[i][0] = false;
for(int i =1;i<=len2;i++)
if(dp[0][i-1]&&s2[i-1]==s3[i-1])
dp[0][i] = true;
else
dp[0][i] = false;
for(int i =1;i<=len1;i++)
for(int j = 1;j<=len2;j++)
if(dp[i-1][j]&&s1[i-1] == s3[i+j-1])
dp[i][j] =1;
else if(dp[i][j-1]&&s2[j-1] == s3[i+j-1])
dp[i][j] =1;
else
dp[i][j]=0;
return dp[len1][len2];
}
};