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leetcode_java/src/main/java/LeetCodeJava/DynamicProgramming/DecodeWays.java
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| package LeetCodeJava.DynamicProgramming; | ||
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| // https://leetcode.com/problems/decode-ways/description/ | ||
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| public class DecodeWays { | ||
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| // V0 | ||
| // IDEA : DP | ||
| // TODO : implement | ||
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| // V1 | ||
| // IDEA : DP | ||
| // https://leetcode.com/problems/decode-ways/solutions/4456554/character-state-machine-video-solution-java-c/ | ||
| public int numDecodings(String encodedString) { | ||
| char s[] = encodedString.toCharArray(); | ||
| if(s[0] == '0')return 0; | ||
| int sz = s.length; | ||
| int noWaysAtIndx[] = new int[sz]; | ||
| noWaysAtIndx[0] = 1; | ||
| for(int indx = 1; indx < sz; indx++){ | ||
| char currC = s[indx], prevC = s[indx-1]; | ||
| if(currC == '0' && !(prevC == '1' || prevC == '2')){ | ||
| return 0; | ||
| } | ||
| int onesDigit = currC - '0', tensDigit = prevC - '0'; | ||
| int number = tensDigit * 10 + onesDigit; | ||
| if(number >= 10 && number <= 26){ | ||
| if(indx >= 2) | ||
| noWaysAtIndx[indx] += noWaysAtIndx[indx-2]; | ||
| else | ||
| noWaysAtIndx[indx] = 1; | ||
| } | ||
| if(number != 10 && number != 20){ | ||
| noWaysAtIndx[indx] += noWaysAtIndx[indx-1]; | ||
| } | ||
| } | ||
| return noWaysAtIndx[sz - 1]; | ||
| } | ||
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| // V2 | ||
| // IDEA : DP | ||
| // https://leetcode.com/problems/decode-ways/solutions/4454539/decode-ways-java/ | ||
| public int numDecodings_1(String s) { | ||
| int n = s.length(); | ||
| int[] dp = new int[n + 1]; | ||
| if(n == 0 || s.charAt(0) == '0') return 0; | ||
| dp[0] = 1; dp[1] = 1; | ||
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| for(int i = 2; i <= n; i++){ | ||
| // check for single-digit | ||
| if(s.charAt(i - 1) >= '1' && s.charAt(i - 1) <= '9') dp[i] = dp[i - 1]; | ||
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| // check for two-digits | ||
| if(s.charAt(i - 2) == '1') dp[i] += dp[i - 2]; | ||
| else if(s.charAt(i - 2) == '2' && s.charAt(i - 1) >= '0' && s.charAt(i - 1) <= '6') dp[i] += dp[i - 2]; | ||
| } | ||
| return dp[n]; | ||
| } | ||
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| } |