[LeetCode] 039: Jump Game II

[Problem]

Given an array of non-negative integers, you are initially positioned at the first index of the array.

Each element in the array represents your maximum jump length at that position.

Your goal is to reach the last index in the minimum number of jumps.

For example:
Given array A = [2,3,1,1,4]

The minimum number of jumps to reach the last index is 2. (Jump 1 step from index 0 to 1, then 3 steps to the last index.)

[Solution]

class Solution {
public:
    int jump(int A[], int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
    
    // invalid
    if(n <= 0)return INT_MAX;
    
    // initial
    int *dp = new int[n];
    int *next = new int[n];
    for(int i = 0; i < n; ++i){
        dp[i] = INT_MAX;
    }
    
    // dp
    dp[n-1] = 0;
    next[n-1] = n-1;
    for(int i = n-2; i >= 0; --i){
        int j = 1;
        while(j <= A[i] && i + j < n){
            // reach the last index
            if(i + j == n - 1){
                dp[i] = 1;
                next[i] = n-1;
                break;
            }
            
            // reach a position which can jump to the last index
            else if(dp[i+j] != INT_MAX){
                if(dp[i] > dp[i+j]+1){
                    dp[i] = dp[i+j] + 1;
                    next[i] = i + j;
                    j = next[i+j] - i;
                }
            }
            else{
                j += A[i+j] + 1;
            }
       }
   }
   return dp[0];
    }
};

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