[LeetCode] Interleaving String

Given s1, s2, s3, find whether s3 is formed by the interleaving of s1 and s2.

For example,
Given:
s1 =

"aabcc"

,
s2 =

"dbbca"

,

When s3 =

"aadbbcbcac"

, return true.
When s3 =

"aadbbbaccc"

, return false.

DP.

class Solution {
private:
bool f[1000][1000];
public:
bool isInterleave(string s1, string s2, string s3) {
// Start typing your C/C++ solution below
// DO NOT write int main() function
if (s1.size() + s2.size() != s3.size())
return false;

f[0][0] = true;
for(int i = 1; i <= s1.size(); i++)
f[i][0] = f[i-1][0] && (s3[i-1] == s1[i-1]);

for(int j = 1; j <= s2.size(); j++)
f[0][j] = f[0][j-1] && (s3[j-1] == s2[j-1]);

for(int i = 1; i <= s1.size(); i++)
for(int j = 1; j <= s2.size(); j++)
f[i][j] = (f[i][j-1] && s2[j-1] == s3[i+j-1]) || (f[i-1][j] && s1[i-1] == s3[i+j-1]);

return f[s1.size()][s2.size()];
}
};