Trace s = "leetcode", wordDict = ["leet","code"].
dp[0] = true (empty prefix)
i=1: "l" not in dict. dp[1] = false. i=2: "le" not in dict. dp[2] = false. i=3: "lee" not in dict. dp[3] = false. i=4: dp[0]=true and "leet" in dict. dp[4] = true. i=5: "c","ec","etc" not in dict. dp[5] = false. i=6: dp[6] = false. i=7: dp[7] = false. i=8: dp[4]=true and "code" in dict. dp[8] = true.
Answer: true.
where is max word length for substring comparison. space.