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Time Complexity will be O(n) because the "start" and "end" points will only move from left to right once. Sliding Window: Use a count to denote the di 阅读全文
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这题考点在于需要设置两个visited数组 Two Queue and add all the Pacific border to one queue; Atlantic border to another queue. Keep a visited matrix for each queue. I 阅读全文
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Backpack problem: dp[i][j] means if the first i elements can sum up to value j dp[i][j] = dp[i-1][j] || (j>=nums[i-1] && dp[i-1][j-nums[i-1]]) the res 阅读全文
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My Solution: Highest votes in discussion 阅读全文
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A slice (P, Q)其实就是从P到Q的序列,(P,Q)是arithmetic slice要求是等差数列且至少有三个数,问array里面有多少个这样的(P, Q) 这道题难点在于想到用DP,一旦想到用DP,就迎刃而解 dp[i]表示以i结束的slice有多少个 阅读全文
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The above image represents the elevation map [[1,4,3,1,3,2],[3,2,1,3,2,4],[2,3,3,2,3,1]] before the rain. After the rain, water are trapped between th 阅读全文
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Greedy + Stack: 用一个栈维护最后要留存下来的digits 需要注意的是:如果遍历到string的某个char, string后面的char数刚刚好能填满这个栈,那么即使这个char比栈顶还要小,也不出栈,直接入栈 最后要删除leading 0 用char[]实现栈,思路一样,要快很多 阅读全文